Despite their aura of mystery and antiquity, petroglyphs are relatively common. It has always amused me that scientists have spent so much time and effort trying to decipher them. If I painted a sign or put my initials on a rock, it would be called graffiti but scientists a 1000 years from now would likely attribute some religious significance to my rock art doodles. It is entirely possible that some petroglyphs have an underlying profound meaning. It is also just as possible that they were made by someone with time and their hands and a convenient rock, for all we know, the above says something like John loves Kate.