In college, we'ed leave messages on friends whiteboards with runes. Back in '93, there weren't a lot of 'nerd' girls, so it was usually a pretty safe way to hide in plain sight. Much better than a tie on the doorknob. Granted, it wasn't Ultima or LOTR, but Beowulf in the Olde English class that we would cite, because nerdy wasn't cool back then.