There's a painting in Lascaux Cave that has a negative image of a hand surrounded by a red nova that could have been created by modern spray paint. The red fades into the rock behind it at different lengths around the circle before it disappears completely. The middle two fingers are a little close together, and look as if the artist had injured or deformed fingers. Both of these being a great possibility along with the possibility that the human hand has simply evolved from what it used to be.
This piece seems to me that it should win an award for first graffiti. It looks as if someone put their hand up against the wall and spray painted over their hand which could be the first 'Ug was here' graffiti. This makes me wonder what was the point of him making the little hand print. And did he get punished for it?
Maybe it was supposed to be part of a bigger picture, but this is certainly quite different from the largely animalistic nature of the rest of the paintings in the cave. If this wasn't graffiti, maybe it was that kindergarten project in which you're supposed to make a turkey out of your hand, or perhaps it was simply artistic experimentation with the primitive air brush. Either way, I love to think of it as the first artistic practical joke.