You can also do body painting with woolite that will show up under a black light. It is a really cool technique, though I do not know if it has any health ramifications.
There is a new trend of non-destructive graffiti that we are finding fascinating. Another cool example is "clean tagging" as seen here: http://talentspeaks.com/index.php/2006/12/11/clean-walls-leave-messages/
http://talentspeaks.com/index.php/2006/12/11/clean-walls-leave-messages/