Abstract: The device comprises a casing in the form of a circular ring having two conically converging outer surfaces provided with symbols and two identical circular discs inserted in the casing and provided each with an arrow. The discs which lie in parallel planes are held together by a bolt and are rotatable in the casing independently of each other in both directions. On the inner side of the casing there are provided recesses, the number of which corresponds to the number of the symbols. In each disc there are provided locking means, which reenter in one of the recesses for locking the disc during its rotational movement.