The Royal Order of the Holy Mackerel / fez design / tattoo
Misc
Stan has been to prison/jail at least 3 times: pool jail for roughhousing, the county jail for making counterfeit money, and a Columbian prison for an unknown reason. Maybe we'll find out that he's been locked up in more than 3 places. You can read more about this here. No wonder he hates the government.
In Bottomless Pit - Voice Over, it's hinted that Stan may have kissed a pig sometime in his shady past.
Stan thinks, as revealed in The Legend of the Gobblewonker, that marriage is terrible. So when he got a 3 on Mabel's dating quiz in MGT Dating, maybe he was celebrating the fact that his score was not higher.
Stan's room contains several strange objects, including a wedding ring (possibly he was going to propose to Carla, possibly a reminder of his brother), a box full of keys (with the words "old" and "stubborn" on it) and a picture of people's feet, while they appear to be boxing.
Stan does not express his feelings easily. So it's kind of shocking in The Golf War to see him supporting Mabel so easily and wholeheartedly. Sure, it could just be another way to show his love for the kids, but I have a hunch that it means he already HAD a rivalry with the Northwests. He is already shown to have had conflicts with many people in power, and he would not give in to Pacifica's demands in Irrational Treasure. Maybe, if my theories are correct and Stanley is the author, Stanford already knew about Nathaniel being a fraud.
Stan drops a hint at his past in Little Gift Shop of Horrors. He starts with watching a movie and ends with raising a kid and your life falling apart. I think what happened here is that Stanley accidentally had a kid (Mr. Pines) with someone, and raising him caused his life to fall apart.
knowledge
Stan seems to know about the anomalies of Gravity Falls. For instance, in Headhunters, he thought Wax John Wilkes Booth had killed Wax Abraham Lincoln, which could easily be true considering that the wax figures are alive.
In Double Dipper, we see Stan having fixed up the copy machine in his office. It's fairly likely that Stan knew that it could copy human beings, especially considering his knowledge of Gravity Falls's dark side. He must have known that he was taking a HUGE chance on Dipper and Mabel discovering the true nature of the copy machine. Note that the pinball machine and the electron carpet from future episodes are also Gravity Falls anomalies housed in the Mystery Shack.
Throughout Boyz Crazy, Stan stocks up in meat and gold for an upcoming apocalypse. I'm very confused as to what exactly will be coming up, or even if this means anything.
In Dreamscaperers, Stan (in his memory) explains to Dipper the power of the mind. When Dipper mentions Bill, neither Stan nor Soos is surprised.
In DGTTU - The Hide-Behind, Stan says that the people of Gravity Falls "are literally the dumbest people in the world. Literally." In context, he is trying to tell Dipper that the Hide-Behind is not real, and trying to keep him from discovering it and the other secrets of the town.
This theory is proven in Scaryoke. He knows about the town's secrets. He says "the one thing I know about that weirdness is that it's dangerous." I think this is a reference to his brother Stanley, who he lost with the help of Gravity Falls's dangerous weirdness.
