This page is about the Blind Eye Society itself. It is not to be confused with the episode.
The society is first mentioned in Gideon Rises with the cryptogram "Search for the blindeye." I think it was referring to the images in Dipper's Guide to the Unexplained.
The symbol is obviously seen in said images. It is also seen early in The Golf War, on a wall next to the Hermanos Brothers Restaurant, and in Soos and the Real Girl, on the side of a dumpster.
I feel that the McGucket hoax was symbolism for the Blind Eye Society. Just like the society keeps people from seeing the truth of the anomalies in Gravity Falls, the McGucket hoax kept us fans from seeing the truth of the author's identity.
After the episode Society of the Blind Eye, we can learn a lot about the society itself. For instance, there is a code on the blindeye page of the journal that says "If my suspicions are correct, this is the work of Fiddleford. Does he really have to go to such great lengths to forget?" This proves that either a) the author was around long enough to see the blindeye, or b) the author had already disappeared and someone else wrote the coded message. Note, though, that it does not say anything about the Blind Eye Society.
The society makes a lot of references to the Great Seal of the United States, found on the back of the $1 bill. For instance, the chant they perform just before they erase Lazy Susan's memory is "Annuit coeptis, novus ordo seclorum." In Latin, it means that a higher power (God) approves of the New World Order (in the dollar's case, the USA.) Also, the all-seeing eye on top represents God watching and giving his knowledge to mankind. But on the wall in the society's meeting area, they have the pyramid with the all-seeing eye facing up... keeping that knowledge from mankind. Exactly what the society wants to do! It may also show that they have (or had) a conflict with Bill.
