This is the underside of a footbridge at the park where we went to a secular homeschoolers gathering today. It's chalk. Also, correct me if I'm wrong but I don't see a single swear word or penis caricature - just sayin'. Made me smile.
Also, on a completely unrelated note, does anyone have any idea why Emmett runs up to this thing at the library every time we go there, and yells gleefully, "ELMO!!!" Because I've tried but I really can't see any resemblance.