User blog comment:Crossc36/Stan's Tattoo/@comment-3075253-20140828043635

The full symbol was revealed in his underground lab, which appeared to be imprinted on the side of his desk. I honestly have no idea what it could mean, but as to why Stan has it is probably related to the secret society he was likely once apart of. It's been confirmed there is a society operating out of Gravity Falls, and from the Season 2 advertising we've gotten their symbol is the "blind eye" we glimpsed at the end of Dipper's Guide to the Unexplained (The Blindeye Society is the term everyone has coined at this point.) My guess is the tattoo Stan has received is obligatory for society members as a means of who is a member, however I'm guessing there was some sort of falling out with the group and Stan (he says in one episode that the guys in his lodge "no longer like or trust him.") It's all speculation, but I'm guessing we're going to be confronted with the tattoo very soon.