Glow in the Dark Tattoos
The new technique uses blacklight reactive ink which only shows up when exposed to UV light. It is perfectly safe and has FDA approval. You can now tattoo to your heart's content and no one would ever know--unless you went out to play underneath a blacklight.
Implications - Imagine showing up in a nightclub and having a glowing tattoo? I think that this kind of spectacle would have club-goers going crazy with excitement and envy. It is no wonder there aren't more of these backlight-reactive body art pieces.