UV tattoo ink is one of the only inks that have been approved by the FDA (for animal use). They’ve been used for a long time in livestock. Not that that should make you comfortable with sticking into your skin or anything, but it’s probably not quite the same as powdering your face with radium.

While we’re on the subject of historically misguided applications of radioactive materials: ever heard of uranium glass? People get real weird around spicy rocks.