- 1 TACTILE MARKER FIELD OF THE INVENTION 5 This invention relates to a tactile marker of a type that is positioned on a walkway surface for the assistance of pedestrians generally and, in one of its applications, for the assistance of persons with impaired vision. 10 Such markers (which are known also as tactile ground surface indicators) typically are arrayed in a grid pattern to mark some sort of transition, for example at the foot or head of a stairway, at the loading area of an escalator or travelling footway and along the edge of a 15 railway platform. However, it will be understood that the tactile marker may be used in other situations, for example as lane markers and boundary markers. Therefore, in the context of the present invention the term "walkway" is to be understood as embracing pedestrian ways and 20 vehicular passageways and roadways such as are capable of accommodating walkers. BACKGROUND OF THE INVENTION 25 There basically are three different types of tactile marker. One is in the form of a tile-like pad that is moulded from a durable plastics material and which incorporates a square array of integrally moulded individual markers. The pad in use is positioned within a 30 recess in a walkway surface. The second comprises an individual marker that has a stem portion that is forced into one of a grid of drilled holes in a walkway and an 2859787_1 (GHMatters) P77133.AU.2 -2 integrally moulded enlarged head portion that sits on the walkway surface. The third type is similar to the second, except that a plurality of aligned markers is moulded integrally with a common depending rail, and the rail is 5 forced into one of a number of parallel channels that is cut into the walkway. The first type of marker suffers the disadvantage that a recess must be provided in a new walkway surface or be cut 10 into a pre-existing surface to accommodate the pad. Also, the pad presents less attractively than a grid of individual markers. The markers of the second type present better as a grid of individual markers but, being moulded from a plastics material, the stems sometimes are not 15 adequately retained in the drilled holes. Various attempts have been made to profile the stems to provide for better force-fitted engagement in the drilled holes, but the plasticity and/or profile of the stems of prior art markers have or has militated against long-term secure 20 engagement. The third type of marker is perceived as being unsatisfactory in at least some situations, due to the unavoidable displaying of the rail that interconnects all of the markers in a given row. Also, in some situations, for example in carpeted floors, the cutting of slit-like 25 channels is either impossible or unacceptable. SUMMARY OF THE INVENTION Broadly defined, the present invention provides in first 30 aspect a tactile marker that is formed at least predominantly from a plastics material and which comprises a head portion that is arranged in use to sit on a walkway 28597871 (GHMatterS) P77133AU.2 - 3 surface and a depending stem that is formed integrally with the head portion and is arranged in use to locate as a press fit within a hole in the walkway. The depending stem is formed along at least a portion of its length with 5 a plurality of barbs, and each barb has a land that is at least partially or generally annular and a portion that is at least partially or generally conical is formed integrally with the land. The portion has a cross-section that reduces in diameter in a direction away from the head 10 portion. The marker typically is arranged such that when the depending stem is pressed or otherwise forced into the hole, the peripheral portion of the land of each barb will 15 be deflected upwardly and inwardly, causing a tensile stress to be induced in the integrally formed conical portion and a radially inward reactive force to be exerted on the periphery of the barb by the surrounding wall of the hole. The magnitude of this reactive force may 20 increase with any attempt to withdraw the marker from the hole, this providing for secure anchoring of the marker in the hole. The head portion of the tactile marker may have any shape, 25 for example a generally cylindrical or domed shape, that will be sensed, when walked upon, as marking a transition from a smooth walking surface. However, the head portion desirably has a generally frusto-conical shape and, most desirably, has an upper surface that is formed with a 30 plurality of anti-skid projections. Such projections, when provided, may optionally be in the form of small cylindrical projections or nodules. 2859787_1 (GHMatters) P77133.AU.2 - 4 The tactile marker may be moulded from any one of a number of thermoplastic materials, including nylon, but desirably is moulded from polyurethane. 5 Longitudinally extending splines may optionally be formed integrally with the stem portion of the marker for the purpose of engaging with the surrounding wall of the hole into which the stem is in use pressed. 10 The splines may be provided to inhibit rotational movement of the stem portion about its longitudinal axis. The peripheral margin of at least some of the barbs may be formed with a flat chordal region and such chordal regions 15 may be displaced by 90* on successive, adjacent barbs. In one embodiment the barbs and the longitudinally extending splines project to approximately the same distance from an axis of the depending stem, which may be 20 solid. For some, but not necessarily all, applications of the tactile marker, a metal cap may be provided to cover the head portion of the marker. 25 The metal cap may be formed from pressed metal and, also, be formed also over a major part of its surface area with a plurality of protuberances as an alternative to the upper surface the head portion being formed with the anti 30 skid projections. 2859787_1 (GHMatters) P77133.AU.2 - 5 The present invention provides in a second aspect a tactile marker formed at least in part from a plastics material and comprising: a head portion that is arranged to sit on a walkway 5 surface; and a depending stem that is formed integrally with the head portion and is arranged to be located as a press fit within a hole in the walkway, the depending stem being formed along at least a portion of its length with a plurality of barbs, and each barb having: 10 a land that is at least partially annular; and a portion that is at least partially conical and is formed integrally with the land, the portion having a cross-section that reduces in diameter in a direction away from the head portion; 15 wherein the marker further comprises at least one formed integrally and longitudinally extending spline for the purpose of engaging with the surrounding wall of the hole into which the stem is in use pressed. 20 The at least one barb may comprise a chordal region such that, when the depending stem is inserted into the hole that is charged with an adhesive, at least some of the adhesive will flow past the chordal region. The tactile marker may comprise a plurality of the barbs comprising 25 the chordal region and the chordal regions may be flat and/or are displaced by 900 on successive, adjacent barbs. The head portion may have an upper surface that is formed integrally with a plurality of anti-skid projections. 30 28597871 (GHMatters) P77133.AU.2 -6 The invention will be more fully understood from the following description of an illustrative embodiment of the tactile marker. The description is provided with reference to the accompanying drawings. 5 BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 shows a perspective view of the tactile marker, 10 Figure 2 shows a view similar to that of Figure 1 but with the tactile marker rotated through approximately 450, Figure 3 shows a sectional view of a stem portion of the tactile marker as seen in the direction of section plane 3-3 in Figure 2, 15 Figure 4 shows a sectional view of the stem portion of the tactile marker as seen in the direction of section plane 4-4 in Figure 2, and Figure 5 shows an end view of the tactile marker as seen in the direction of arrow 5 in figure 2. 20 DETAILED DESCRIPTION OF A SPECIFIC EMBODIMENT OF THE INVENTION As illustrated, the tactile marker comprises a generally 25 frusto-conical marker head 10, having a bevelled surround 11 that extends to a marginal rim 12, and an integrally moulded stem 13 projecting downwardly from the underside of the head 10. The tactile marker in accordance with the exemplified embodiment is formed entirely from a 30 thermoplastics material such as polyurethane and the head portion is arranged in use to sit on a walkway surface 2859787_1 (GHMatters) P77133.AU.2 - 7 (not shown) with the depending stem located as a press fit within a hole in the walkway. The upper surface of the head portion 10 is provided with 5 a plurality of integrally formed anti-skid projections 14 which, as illustrated, are in the form of small cylindrical projections. The stem 13 is formed along its length with five axially 10 spaced barbs 15 to 19, the lowermost one of which comprises a generally conical end portion of the stem 13. Also, the stem is formed between the uppermost barb 15 and the underside of the head portion 10, with four longitudinally extending splines 20. 15 Each of the barbs 15 to 19 comprises a generally annular land 21 having an outer peripheral margin 22 and, formed integrally with the land, a generally conical portion 23. The conical portion associated with each of the lands 21 20 is, as shown, located below the land and has a major diameter that is the same as (or approximately equal to) that of the land, and the conical portion 23 has a cross section that reduces in diameter in a direction away from the head portion 10. 25 The dimensions of the various parts of the tactile marker will be determined by particular applications to which the marker might be put. However, in one embodiment of the marker the barbs 15 to 19 may have an outside diameter of 30 9.5mm and the depending stem will in use be pressed or otherwise forced into a drilled hole having a diameter within the range 8.0mm to 8.5mm. As indicated previously, 2859787_1 (GHMattn) P77133.AU.2 -8 with such an interference fit, when, in use, the depending stem is pressed into the hole, a peripheral portion of the land 21 of each of the barbs will be deflected upwardly and inwardly, to cause a tensile stress to be induced in 5 the conical portion 23 and a radially inward reactive force to be exerted on the peripheral margin 22 of the barb by the surrounding wall of the hole. Thus, the stem 13 will be held captive against longitudinal displacement from the hole by the barbs 15 to 18 and will be held 10 captive against rotation within the hole by the splines 20. The splined region of the stem has the same effective diameter as the barbs and, thus, also engages with an interference fit in the hole. 15 Also, in order to enhance retention of the stem in the hole, an adhesive may in some circumstances be inserted into the hole before the stem is inserted. Then, in order that the adhesive, when used, might flow along the full length of the stem and provide for maximum anchorage, the 20 land 21 of each of the barbs is formed with two diametrically disposed flat chordal regions 24, and the chordal regions are displace by 900 on successive adjacent barbs. 25 In the claims which follow and in the preceding description of the invention, expect where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, 30 i.e. to specify the presence of the stated feature but not to preclude the presence or addition of further features of the invention. 2859787_1 (GH Matters) P77133.AU.2