| 摘要 |
The signboard, e.g. traffic sign, comprises a base of which the upper surface is provided with parallel triangular-section grooves. The (45 deg.) isosceles sides of the triangular-section ridges so formed carry the signs, e.g. all left hand sides one sign and all right hand sides another sign. - This surface is coated with transparent plastics, the total thickness of the board not exceeding 5 mm. The observer sees one or the other sign depending on the angle of view.
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