A guy I know who used to typeset ads for our local paper used to get so bored he'd slip in some of his own. Ones like: "For sale, one pair of gloves (left one missing)"; "For sale, Santa suit, blue"; and the one I like best, though I don't know why - "For sale, clothes line, used, needs attention".

They used to get in the paper, too, though I don't know whether there ever any reponses.