About those Sharpies...
Did you know that green Sharpie residue on skin (as in, marked, and then washed mostly off with soap and water) will glow that sort of sickly firefly yellow-green under blacklight? More of the coolness (and possiblie toxicity) of Sharpies. Don't know what you'd get with different colors, though.
(discovered after this SM had experimented with "tattoo" possibilites for her show, and walked through lighting work the next day)
While this is mostly useless trivia, I figured if anyone would ever need it, it would be this group!