I wonder if some ancient primitive ever considered that thousands of years in the future a bunch of heritage starved "modernists" were going to fawn over his equivalent of sketching in the margins.
:') Petroglyphs were some kind of symbolic system, but only some of the time. Probably. They're either so old that the people who used to make them died off, or were killed off by their PreColumbian neighbors, or weren't easy enough to use and teach that they arose a number of times and croaked out each time.
It was prolly just some stone age gangstas taggin' their turf.