WO1996012266A1

WO1996012266A1 - Systems for information-carrying signs

Info

Publication number: WO1996012266A1
Application number: PCT/NL1995/000357
Authority: WO
Inventors: Johan Kok; Siete Fijma; Franciscus Schoofs; Gerardus Van Zanen
Original assignee: Johan Kok; Siete Fijma; Franciscus Schoofs; Gerardus Van Zanen
Priority date: 1994-10-17
Filing date: 1995-10-17
Publication date: 1996-04-25
Also published as: DE69514695D1; EP0871947A1; NL9401728A; EP0871947B1

Abstract

The system is composed of signs, means for securing the system to the immobile world and coupling means. Signs according to the invention consist of a front shield and a back shield which can be rapidly fastened to each other by means of a locking system operated by a special key. The signs can be rapidly interconnected according to a fixed pattern by means of a standard coupling piece. All connections are invisible and inaccessible for unauthorized persons. The front shield comprises an integrated reflector and does not use costly retroreflecting foils. Important advantages of the invention are its resistance against vandalism, low purchasing and managerial costs, rapidity and flexibility in use and, finally, a nice and quiet appearance.

Description

Systems for information-carrying signs

Field of the invention

The invention relates to systems for information- carrying signs, in particular (but not exclusively) for traffic signs.

The invention concerns the pattern of the systems, the design of the signs, the means for securing the systems to the immobile world, the coupling of the signs to each other, the operating tool and the type of retroreflection of the signs.

Backgrounds. State of the Art

(Traffic) signs consisting of a shield (usually metal) , often with a double-flanged rim (DFR) and separate fastening means (clamps) , are known and generally used. On the front side of the shield, foils and/or layers of lacquer are applied, retroreflecting or otherwise, representing information such as, for example, traffic symbols.

The shield and fastening clamps are often fixedly interconnected by clamping screws. The clamps are in turn secured to posts, walls or other parts of the immobile world by clamping strips or screwed connections. Various types of bridging structures between the shield(s) and the immobile world are also often used. Many aspects of the design of traffic signs are outlined in the NEN-standard 3381. A European standard is in preparation (CEN/TC 226 N125) .

Both standards are based to a great extent on the current state of the art. Although plastic is not excluded as a sign material, the requirements depart from metal. The retroreflection requirements depart from a sign with a retroreflecting foil.

A disadvantage of the sign design described above, is that (even without considering the often necessary earthwork) the installation, changing, replacing and removal of the signs are very time-consuming because of the many elaborate connections to be made/broken. The current design also has the disadvantage that the signs cannot be put into service flexibly. If, for example, in the case of temporary, periodical and/or unexpected changes in a traffic situation, changes of symbols or additional signs are required, such an alteration can usually not be carried out instantaneously and without any preparations.

Research (e.g. "Kostenvergelijking van retroflecterende materialen" (Comparison of the costs of retroreflecting materials), Grontmij, 1989) has shown that damage to (traffic) signs constitutes a costly problem in many places. 45% of the signs are prematurely replaced because of damage.

Damage is usually the result of vandalism and accidents. Important elements of vandalism are theft, graffiti and destruction.

The current sign design allows theft because the fastening means (such as bolts and nuts) can be easily reached. After theft, a new sign has to be purchased and installed.

In spite of many efforts, an effective means of preventing graffiti on signs has not yet been found. Consequently, a sign covered with graffiti has to be replaced or renovated, which again leads to additional installation costs and/or purchasing costs. Destruction often involves beating, pulling and/or hanging on the sign. The double-flanged rims of common signs have been found not to be strong enough to resist these destructive forces, so that these signs often bend or dent, as a result of which the sign becomes unusable according to the standard. Replacement then is the only solution.

Summarizing it may be said that current signs have the disadvantage of being susceptible to damage and that the costs of repairing the damage incurred are high. Not only does the common double-flanged rim not provide enough rigidity to a sign, it also has the disadvantage of being open and making the sign susceptible to accumulation of dirt and corrosion. Often, sign combinations (several signs) are required in one place (e.g. on one post) . Until now, no universal solution for this mounting problem has been found. The current sign combinations are often tailored to each new situation and consist of clamps and/or combinations of tubes and coupling pieces.

From a managerial point of view, the current situation is disadvantageous in logistic and financial respect: there are many different parts and each sign combination requires a lot of attention.

The back sides of the current sign combinations present complex structures which make a chaotic impression and which do not fulfil the design requirements that other pieces of street furniture often have to meet. Known are retroreflecting foils, applied to the front side of the sign-shield. In the Netherlands (and in many other industrialized countries) these foils are used on a large scale as they contribute considerably (in the dark) to the visibility/readability of signs and thus promote traffic safety.

Retroreflecting foils are available in many different embodiments. Their principle of action is based on (glass) beads or on so-called cube-corner elements.

The requirements as regards the reflection performance of signs, as outlined in the current standards and legislation, are based to a great extent on the properties of retroreflecting foils that have been available until now. The reflection performances of retroreflecting foils are subdivided into classes I and II (recently also: III) . The higher the class, the better the performance. The life span related to reflection also increases with class. The requirements as regards the reflection of signs differ for each application. It is, for example, generally accepted that signs within a built-up area have to provide maximal reflection at a distance of 50 meter. It is known that the design of cube-corner reflectors can be optimized for a specific application.

It is also known that for larger angles of observation, the reflection performance of many reflectors with cube-corner elements is inferior to that of glass-bead materials (usually foils) . This makes cube-corner reflectors less fit for application in signs designed for situations in which the angles of incidence and observation are relatively large (e.g. the narrow streets of inner cities) .

Generally applied methods of representing information (e.g. traffic symbols) on said retroreflecting foils, consist in printing and/or sticking onto them transparent or black lacquers and/or foils. It is characteristic of current signs that retroreflecting foils contribute_considerably to the total cost price. This disadvantage applies most to foils of class II.

Objects of the invention

It is an object of the invention to eliminate and/or reduce the above-mentioned disadvantages. The invention aims:

• to reduce the managerial costs associated with the signs, since

- placing, changing, replacing and removing the signs takes less time and preparation than today,

- the number of different system parts is smaller than today, which allows a reduction of stores with the materials manager,

- the resistance against vandalism is greater than that of current signs, resulting in less damage,

- the expected life span related to the reflectance of the signs is higher than that of current signs, which results in a delay of the purchase and installation of a new sign,

- in the case of replacement, usually only a relatively cheap front shield, rather than a complete sign, needs to be purchased;

• to enlarge the user comfort for mechanics, since - the sign parts (front and back shields) are now capable of being nested and stacked,

• to realize a lower cost price for the product

- by providing an optimal reflection of the signs for each area of application (in the order of, but not necessarily exactly matching the reflection classes I and II) , without using the relatively expensive, commercially available retroreflecting foils such as, for example, Schotchlite Engineering Grade and High Intensity Grade of the firm 3M, - by standardizing systems parts (more than is done today) , so that the production numbers per part can be increased and the stocks required can be reduced,

- by integrating the provisions for coupling the signs largely into the back shield, so that coupling can be realized by means of a simple (and cheap) coupling piece;

• to increase traffic safety, since

- the material manager can respond more quickly to temporary or unexpected changes in traffic situations (involving the necessity to change or add symbols) , - damaged signs can be replaced more quickly,

- as opposed to current signs, the signs according to the invention possess a high reflectance standard, which promotes a general application of retroreflecting signs,

- a sign can now be tailored to a specific situation, thanks to a special reflector design,

- the back sides of the signs have a quieter appearance and thus create a simpler and safer overall traffic picture.

• to improve the quality of the public space

- by improving the design of the signs, - by standardization (creating more unity in the townscape) .

Description of the invention

The invention will be further explained below with reference to the exemplary embodiments represented in the drawings.

First, a brief enumeration of the figures will be given.

Fig. 1 shows different views of a possible combination of system elements according to the invention: signs, coupling pieces and means for securing the system to the immobile world.

Fig. 2 shows front and top plan views of a composite circular sign according to the invention, mounted on a sign post. One coupling has been mounted on the side of this sign.

Fig. 3 shows section Al-Al of fig. 2 in detail, representing the rim connection between the front and back shields.

Fig. 4 shows front and top plan views of a circular front shield according to the invention.

Fig. 5 shows section A2-A2 of fig. 4 in detail.

Fig. 6 shows front and top plan views of a circular back shield fitted with a locking system, all according to the invention, in which coupling pieces are mounted on the back shield in one coupling direction. The back shield in turn is mounted on a sign post.

Fig. 7 shows section A3-A3 of fig. 6 in detail. Fig. 8 shows section B-B of fig. 2 in detail, schematically representing a mechanism for transmitting forces from the front shield to the back shield.

Fig. 9a shows section D-D of fig. 6.

Fig. 9b shows a part of the same section D-D, positioned back to back with figure 9a. This illustrates the back-to-back installation of signs against a post, each sign being fastened with its own clamping strips. Between figures 9a and 9b a part of a sign post is shown.

Fig. 10 shows section E-E of fig. 6. Fig. 11a shows section F-F of fig. 9a, in which the clamping strip connection is shown around a tube with the smallest possible diameter.

Fig. lib shows the same section F-F, in which the clamping strip connection is shown around a tube with a relatively large diameter.

Fig. 12 schematically shows a pattern for installing signs according to the invention, in this case with four coupling directions.

Fig. 13 schematically shows a pattern for installing signs according to the invention, in this case with two coupling directions at right angles to each other.

Fig. 14a, 14b, 14c schematically show a single locking lock according to the invention in a top plan view (without the front shield) , a partly cut-away front view and the respective sections G-G, H-H and I-I (partly in elevation) .

Fig. 14a shows the single-locking lock in the closed position, the front shield being pulled and/or locked against the back shield.

Fig. 14b shows the lock during the operation thereof, the front shield being ejected with respect to the back shield.

Fig. 14c shows the situation after the front shield has been taken out.

Fig. 15 shows a front view of a rotating body with a pin according to the invention, positioned in the corner of a triangular back shield.

Fig. 16 shows detail C of fig. 6. The inserted operating tool is shown as well, in two positions.

Fig. 17a and 17b show section J-J of fig. 16.

Fig. 17a shows the locking system (and operating tool) in the closed position.

Fig. 17b shows the locking system (and operating tool) in the opened position.

Fig. 18 shows detail K of fig. 16 in which the tool has been inserted in the winding bush and the locking system is in the closed position.

Fig. 19 shows section M-M of fig. 18. Fig. 20a shows section L-L of fig. 18 (closed position) .

Fig. 20b shows the same section L-L with the system in the opened position.

Fig. 21 shows section N-N of fig. 19, representing the opening for the operating tool in the back shield.

Fig. 1 shows rear, side, top plan and front views of an example of a combination of system elements according to the invention. A sign (1) is secured at the back thereof by means of clamping strips (2) to the immobile world, in this case a sign post (3) . Another sign (4) is connected to the side of sign (1) by means of coupling pieces (5) . Sign (6) is mounted above sign (1) by means of coupling pieces that are identical to (5) . Sign (7) is installed under sign (1) by means of coupling pieces. These views illustrate the closed nature of the signs: from the outside, no fastening means capable of being opened are visible.

Fig. 2 shows top plan and front views of a possible embodiment of the invention. In this embodiment, the sign consists of a information-carrying front shield (8) , which can be fastened all round to a back shield (9) . The back shield can be secured to the immobile world, for example a sign post (3) , or be coupled to other signs of the system through coupling pieces (5) .

Fig. 3 shows a section of a possible rim connection (10) between the front and back shields. This connection is such that both shields, when fastened to each other, together form a rigid box construction, making denting of the sign impossible.

A great rigidity is also necessary because, according to the invention, the coupled signs are not (as has been the case until now) supported by auxiliary constructions.

Fig. 4 shows front and top plan views of the front shield according to the invention. As appears from the section in fig. 5, this front shield consists of 2 parts, a shield (11) and a protection plate (12) .

The shield (11) is made of a clear transparent material, for example a plastic. It is entirely flat at the front and forms a pattern of cube-corner reflector elements (13) at the back, which render the shield retroreflecting.

The reflector elements (13) may be designed in many other (already known) ways, depending on the application of the sign. It is, for example, possible that, for applications within a built-up area, the reflector elements are shaped thus by the back side that reflection is maximal for irradiation by vehicles at a distance of 50 meters from the sign, when the sign is positioned at a height of 2 m above the road surface. At some distance behind said reflector elements, a protection layer or plate (12) is connected all round to the shield (11) so as to form a connection which is impermeable to liquid, the colour of this layer or plate preferably being white. This plate prevents dirt and moist from reaching the reflector elements at the back, and thus from having a negative effect on reflection. Moreover, the white colour enhances the necessary white appearance of the front shield (especially during daytime) , when looked at from angles at which the reflector elements do not reflect but on the contrary can be seen through.

When the reflection properties desired for the sign application cannot be realized through a particular design of the cube-corner reflector elements (13) , retroreflecting foils (14) can be applied to the front shield, according to the currently accepted method. In that case, the material of the front shield does not have to be transparent and the reflector elements on the back side of the shield can be omitted, as well as the protection plate. It has been found that certain (light) types of matting on the front face of reflectors may cause a considerable improvement of the reflection of, in particular, reflectors based on the cube-corner principle, at large observation angles, compared with the situation without matting.

The discovery described above can be useful when applied to retroreflecting signs, for example according to the invention, which are designed for relatively short observation distances (for example within a very densely built-up area) .

Representations of information, such as traffic symbols, are applied to the front shield according to the above-described known techniques (printing, sticking) . For this purpose, known (special) layers such as layers impermeable to UV-light or layers with little affinity for inks (graffiti) may be used as well.

A special embodiment of the front shield is the neutral print, for example a plain grey surface, which can be used when a sign is out of service. Fig. 6 shows a top plan and front view of an embodiment of the back shield (9) according to the invention. The back shield is preferably made of plastic, according the NEN-standard in the colour grey. The back shield comprises on the back side thereof a semi-circular groove (15) , which allows centring this part against a range of round posts with varying diameters (3) . The diameter of the groove is equal to the diameter of the smallest post onto which the sign still has to fit. In some places on both sides of this groove, the back shield comprises openings (16) through which clamping strips (17) can be led in order to press the back shield against the post.

Fig. 9a and 9b show a recess (18) in the groove (15) which allows passing (19) clamping strips between, for example, the sign post (3) and the back shield (9). The embodiment of the clamping strip openings described above allows placing 2 signs back to back, while they are both fastened to, for example, a sign post by means of clamping strips. The lock (20) of the clamping strips is preferably located inside the back shield, instead of outside the back shield (on the post) . This construction renders the clamping strip invisible and inaccessible once the front shield has been installed.

The back shield according to the invention may also comprise provisions to screw two back shields back to back, in particular around the post/tube with the smallest diameter in the above-mentioned range. The heads of the screws used for this purpose and possible nuts are positioned on the front side of the back shield and are therefore inaccessible after the front shield has been installed.

The back shield (and possibly the protection plate) can, if and where necessary, be provided with ribs (21) increasing its rigidity and strength. Apart from the clamping strip openings (16) , the sign is closed all round, so that there is little risk of accumulation of dirt or corrosion.

Fig. 8 shows a schematic section of a central projection (22) on the back shield, prohibiting that a front shield, when pressed backwards from the front side, will bent through. The protection plate (12) comprises one or more projections (23) which transmit the force from shield (11) to protection plate (12) . This protection plate in turn transmits the forces to said projection. Fig. 11a and lib are sections showing how the semicircular groove (15) centres tubes etc. of varying diameters.

Fig. 11a shows the situation of the tube (24) with the smallest fitting diameter. In this case, a sign mounted back to back with the first sign will be flush with the latter. Fig. lib shows the situation in which the sign is clamped onto a round tube (25) with a relatively large diameter. Fig. 9a and 10 show provisions in the back shield (9) , to which coupling pieces (5) for interconnecting the signs can be fastened, for example by means of screws (26) . In the embodiment of the invention shown, a coupling between two signs is realized by means of two elongated coupling pieces, for example tubes. These coupling pieces are put through holes (27) in the back shield (see also fig. 6) , so that the coupling pieces are largely invisible, and the fastening thereof to the back shield completely invisible, once the front shield has been installed. After the installation of the front shield, it is also impossible to reach the fastening means.

A coupling between signs according to the invention matches the shallowness and the geometry of the sign. This coupling also matches the coupling pattern discussed below. It is desirable to install a sign in front of a tube/post by fastening it with coupling pieces to an adjacent sign (usually above or under the first sign) , instead of fastening the sign to the tube/post with clamping strips. This method is time-saving and it also has the advantage of allowing the installation of an additional sign in cases where the tube/post behind the first sign does not extend far enough to allow the use of clamping strips.

A practical embodiment of such a coupling consists of two identical, parallel tubes, rods or strips (5) which can be installed along the post/suspension tube according to fig. 1, 9a and 10.

The embodiment described above is essential for realizing a coupling which has a transparent appearance, which is sufficiently rigid and strong, which does not project in front of the sign surfaces and which allows back- to-back installation of additional signs or sign combinations. Said embodiment in the form of a tube has the additional advantage that coupling pieces can be easily given lengths that deviate from the standard, for example by sawing.

The coupling system according to the invention allows coupling signs in the same plane as the front side of the front shield. In order to restrict the required number of different coupling pieces, the coupled signs are positioned according to a certain spatial pattern.

Within one sign system according to the invention, a two-dimensional, circumscribing geometric basic form (28) can be defined, into which the front faces of all the signs belonging to that system (e.g. a circle (29) , a triangle

(30) , a square (31) , a rectangle (31) , or yet another shape (32, 33)) fit.

A pattern according to the invention is made up of lines (34) representing coupling directions, said pattern also satisfying the condition that at each intersection (35) of these lines, a said circumscribing form can be positioned in such a way that the geometric centre of this circumscribing form coincides with said intersection and that circumscribing forms thus positioned do not overlap. Fig. 12 schematically shows a pattern of sign positioning according to the invention with, in this case, four coupling directions.

Fig. 13 shows another conceivable, and in practice very useful, pattern according to the invention, in which signs can be coupled in the sign plane in four different directions: upwards, to the left, to the right and downwards.

The abutment surfaces/fixation points for the coupling pieces are chosen in such a way that they all fit into the pattern.

Given the large sign dimensions and the expected limited rigidity of separate front and back shields, it is necessary to fasten the shields to each other at several, closely spaced points along the entire circumference of the sign. This construction also makes it virtually impossible for vandals to separate the shields from each other.

The invention therefore provides a locking system, which is intended to pull the front shield (8) and the back shield (9) against each other when the sign is closed.

It is possible that both shield rims, after having been interlocked for a long time, cling to each other as a result of humidity and dirt and consequently cannot be separated by hand. Therefore, the locking system has to be able to force the front and back shields forcefully apart when the sign is opened.

The locking system according to the invention is composed of several single-locking locks (36) (fig. 6) that are spaced along the rim of the sign. This single-locking lock according to the invention can be described as follows. The rim of the protection plate (12) or, in another embodiment, the shield (11) , comprises one or several inclining surfaces which, in cooperation with one or more elements or surfaces moving along these surfaces, connected to the back shield, produce a wedging effect. This wedging effect is two-fold and causes the front shield to be either attracted or ejected with respect to the back shield. In addition, said element/surface can be moved in such a way that it no longer contacts said inclining surfaces, so that the front shield can be moved freely into or out of the back shield.

In fig. 14a, 14b and 14c an embodiment of the single- locking lock is further illustrated.

The inclining surfaces (37, 38) are accommodated in an open slot (39) which has been provided in the rim of the shield (11) or protection plate. The moving element is composed of a pin (40) on a body (41) which is connected rotatably to an axis (42) on the back shield. The pin exclusively moves in a plane perpendicular to said axis. Body and pin are driven by a cable (43) which is fixedly connected to the body and/or the pin, and which can be moved in two directions. It should be noted that the front and the back shield, when they are interconnected, can only translate parallel to the axes (42). The lock further comprises provisions for placing the slots always in a certain position with respect to the axes (42)

Fig. 14a shows the single-locking lock in the locked position: front and back shields are pulled onto each other as the pin (40) abuts on an inclining surface (38) .

Fig. 14b shows the situation in which the pin (40) has been turned towards the right with respect to the situation of fig. 14a, as a result of which the pin has ejected the front shield by way of the inclining surface (37).

In fig. 14c, the front shield has been released from the back shield. In this embodiment, this is made possible by the opening (44) , but it could also be realized by turning the pin (40) further to the right. Many other embodiments of the lock according to the invention are conceivable.

Fig. 15 shows a practically useful embodiment of said moving element of the single-locking lock. It consists of a rotatable body with a pin (45) , mounted in the corner of a triangular sign (46) .

The rotatable body with the pin has been designed in such a way that the operating cable (47) runs along the circumference of a circle segment (48) . According to this essential embodiment, the cable length is constant in each position of the locking system and it is possible to fit the rotatable body in the corners of all conceivable types of signs (including triangular and rectangular signs) .

Since the entire locking system is situated along the rim of the back shield, it is possible to nest back shields having the locking system mounted on them.

From the point of view of user comfort, it is not acceptable when all the single-locking locks need to be operated separately. Therefore, the invention provides a central control of all the single-locking locks. An essential aspect of this control is that all single-locking locks are interconnected in such a way that forces can be transmitted in two directions (opening, closing) and in such a way that the operating force can be fed into the system at one point. Another essential aspect of the central control is that it requires a special key. Fig. 16, 17a, 17b, 18, 19, 20a, 20b and 21 show an embodiment of the central control according to the invention. This control consists of a bush (49) to which the two ends (50, 51) of a cable (43) are fixedly connected, said cable being fixedly connected to all the above- mentioned rotatable bodies with pins (41) . Said cable runs along the rim of the back shield, so that the rotatable bodies can be operated in two directions.

Said bush has been mounted rotatably in the back shield (9) . It can move the cable both to the left and to the right. After the front shield has been installed, the bush can be operated by means of a special key (52) , which can be inserted into the bush through a special opening in the back shield. The key end (54) has a shape which does not resemble any common standard tool (such a screw drivers, wrenches etc.). The bush has a corresponding contra-shape. Since the key is special, the sign can only be opened by authorized personnel. Since all the connections are situated behind the back shield, theft of the sign is made far more difficult. The key shown here can only be withdrawn after the locking system has been put into the locked position.

Claims

1. Systems for information-carrying signs, in particular (but not exclusively) traffic signs, consisting of signs, materials for securing the signs to the immobile world, coupling pieces between the signs and operating tools, characterised in that the signs can be coupled to each other in a plane parallel to the front face of a sign by means of said coupling pieces, wherein all the signs belonging to one sign system can be positioned according to a pattern in said plane, which pattern is made up of lines (and their parallels) , representing all the coupling directions and satisfying the condition that at each intersection of these lines and their parallels, a circumscribing form can be positioned in such a way that the geometric centre of this circumscribing form coincides with said intersection and that circumscribing forms thus positioned do not overlap, said circumscribing form being a geometric basic form into which the front faces of all the signs belonging to said sign system fit.

2. A sign, in particular (but not exclusively) a traffic sign, characterised in that the sign is divided into two matching main parts, namely an information/symbol- carrying front shield and a constructional and partly closed back shield, said front and back shields being fastened to each other by means of a locking system at several points along the circumference of the signs, or along the entire circumference of the signs, so that the front and back shields, once connected to each other, form a rigid box structure.

3. A locking system according to claim 2, consisting of one or more single-locking locks, positioned on the rim of the front shield and/or the back shield (protection plate) , characterised in that the lock or the single-locking locks is/are connected to a central control device, in that the lock or the single-locking locks can attract or eject the front shield with respect to the back shield by a wedging action, and in that the lock or the single-locking locks has/have positions in which the front shield can move freely into or out of the back shield or in which it is fixed with respect to the back shield.

4. A single-locking lock and a connection with the central control device according to claims 2 and 3, characterised in that the single-locking lock consists of a body that is rotatable on an axis on the back shield and/or the front shield, wherein one or several surfaces of this body abutting on surfaces on the front shield and/or the protection plate and/or the back shield, produce wedging actions on and clearance and fixation of the front shield and/or the back shield, wherein said rotating body is driven by a flexible element (such as a cable) which is guided along a cylinder or cylinder segment of the body, the axis of this segment coinciding with said axis of rotation.

5. A central control device according to claims 2 and 3, housed inside the front or back shield in a movable way and mechanically connected to a lock or single-locking locks, characterised in that, once the front shield has been installed, it can only be reached with a special key through an opening in the front or back shield, wherein said key has a "bit-shape" which deviates entirely from that of common tools such as screw drivers, wrenches etc., and wherein the "bit" of said key fits into the control device (as opposed to the standard tools mentioned) .

6. A back shield according to claim 2, characterised in that the back side thereof comprises a semi-circular groove centring said back shield on a range of round posts and or tubes, wherein the diameter of the groove is equal to the diameter of the smallest post/tube onto which the sign has to fit and wherein said back shield comprises openings through which clamping strips can be led and wherein the locks of said clamping strips can be located on the front side of the back shield, and wherein the groove has a larger diameter at the level of the openings so that a clamping strip can be slid between the post/tube and the groove.

7. A back shield, according to claim 2, characterised in that the coupling pieces can be inserted through openings in the back shield (which can be easily provided) , in that they can abut against the front side of the back shield and in that they can be entirely fixed by fastening means from the front of the back shield, said fastening means being inaccessible once the front shield has been installed.

8. A back shield according to claims 2 and 6, characterised in that it is capable of being directly fastened back to back to a second back shield, for example by means of screws, wherein a post/tube can be located between the two back shields, and wherein the fastening means used are no longer accessible once the front shield has been installed.

9. A coupling between signs according to claim 7, characterised in that the coupling does not project anywhere in front of the plane through the front side of the front shield, nor at the back of the plane through the back side of the back shield, in that it consists of two coupling pieces positioned parallel to each other and parallel to the direction of the post/tube, the two coupling pieces being located on both sides of the post/tube (or the imaginary elongation thereof) .

10. A front shield according to claim 2, having a flat front side, made of a clear colourless transparent material, connected at the back in a water-tight way to a white protection plate, characterised in that retroreflection is achieved by integration of cube-corner elements in the back side of the front shield, and that the information and/or symbolic representation on the front side of the front shield is realized by application of transparently coloured or black foils and/or lacquer(s) .

11. A front shield according to claims 2 and 10, characterised in that the front face of this shield has been matted by means of some technique (e.g. casting structure, foil or lacquer) , according to a particular pattern (e.g. plain surface, grid or a particular figure) , with a particular texture.