There was discussion about the skull markings on here quite a while ago...
Apparently they were visible still on google earth photos circa 2002? though faded.
I had always assumed that they were only used in the movie as well, but those people from Victoria are different...
I've always been told as well that the skull was already painted on the road where they filmed it. Had not heard previously that was an "official" marking of any kind, but when you look at how neatly it is laid out, it does look more official than graffiti.
I was also told that it was visible for many years after the film, although no one was ever able to give me a specific location on this one.