The shape of the stones and their relative positions in the old version are unique. The constellation is only found in two republics of former Yugoslavia, Serbia and Macedonia, and nowhere else.
Endemic —that's how they are called— road signs make it possible to determine one's position unequivocally, at least on the country level. The page about Finland f.e. features a small excerpt from our TGGP (†). I do agree that GPS would deliver better precision, but our system mitigates the risk of robbery, is not easily spoofed, and works without batteries.
The modern Falling Rock Signs comes in two versions. The first one counts six stones, the other one only five. The second version is missing the small rock which is drawn closest to the rock face at about one third of the height of the cliff. At first I thought the missing stone was a production error, but as we have found several similar panels, the sixth stone must be left out by purpose — it may be an omission in a check list somewhere during the production.
Notice that the art work display in the Forestry Faculty of Belgrado is composed of the six-stone version of the road sign. We have seen other artefacts inspired by roadsigns in a.o. Basel (Switzerland) and in Riga (Latvia).