Well, everywhere might be overkill but no matter where you go you'll find that people like to leave a record of their having been there. We record out history. We leave graffiti in the most intimate places. We seem to need to let others know that we are or were alive. If you approach the addition of Petroglyphs (actual carvings rather than something simply drawn or painted on the surface) to the walls, floors and/or ceilings of some of the places in your roleplaying campaign setting from the perspective of the person making the carving, you'll find it fun when your players become intrigued and eventually figure out what your alter ego has to say. Read more here!