I have multiple tattoos, only one of which could potentially be visible while I'm interpreting. It's on my upper arm, and even though it is actually the ILY symbol, I still cover it up for work.
I would be very, very surprised to see an interpreter with visible tattoos. It wasn't until I started working at Gallaudet (and taking classes there) that I ever saw pierced interpreters - I know a couple with very tiny nose piercings and several, myself included, with ear cartilage piercings. But tattoos? Never seen it while somebody's been working. When I'm not working I do like to show mine off though!
I've considered getting a wrist/forearm tattoo in white or ultraviolet ink, though. The UV ink tattoos are only visible while they're healing, and after that they are literally invisible except under black light. Depending on individual skin tone, some people get a similar effect with white ink - where you have to look very closely to see it.