Now this is new and so not standardized at all yet but I'd definately consider doing it after it had been widely tested. It makes removal a lot easier
http://abcnews.go.com/Technology/Story? ... 609&page=3
"Anderson has formed a company, Freedom-2, to commercialize the inks, and he hopes to bring the first generation of microencapsulated inks to market in the next year. He adds that the design opens up possibilities for a whole range of specially timed tattoos.
"You could sit around and think of all kind of things, like a time-limited tattoo, one that would last three years and then disappear, or tattoos that only appear at night."