Discover has a huge gallery of science- and engineering-themed tattoos. Some are amazing and some are, well, less so. Above from left, RFID tag, quadratic formula, and LSD. "Science Tattoo Emporium" (Thanks, Marina Gorbis!)
UPDATE: This appears to be a photoset that author Carl Zimmer had uploaded to Flickr a while back but has since moved to the Discover site.