This tattoo was submitted by w m r and reads “quis custodiet ipsos custodes”. From Wikipedia:
Quis custodiet ipsos custodes? is a Latin phrase from the Roman poet Juvenal, which literally translates to “Who will guard the guards themselves,” and is variously translated in colloquial English as “Who watches the watchmen?”
The Watchmen movie is coming out tomorrow; have you read the graphic novel by Alan Moore and Dave Gibbons yet?