... or maybe they were just marking the spot where their favorite hallucinogens were growing with a semiotic that struck them as appropriate given their altered mental state at the time, a sort of prehistoric set of roadsigns to guide them on their trip.
Yeah, it could be early gangsta tagging.
Maybe these were painted around 1969 by stoned hippies from Woodstock. Seems to be an antiwar theme in the patterns with some resembling a peace sign.
Or maybe Burning Man goes back even farther than we thought.