The owner, Texas A&M University, has already sent cease-and-desist letters to people who use the 12th Man name inappropriately.
In fact, the university initially took aim at the Seahawks for using the name. University officials had the business savvy to trademark the term in 1990, and in 2006 they cut a deal with the Seahawks.
Under that deal, the Seahawks paid $100,000 for exclusive rights to use the 12th Man. The team will also pay $5,000 a year until 2016.
That figure might sound cheap in the multi-billion dollar world of the NFL, and Texas A&M may soon want more money. The two sides are renegotiating the deal.
"I can't talk about the nature of those discussions and where we are today, but again, the 12th Man is priceless," said Texas A&M Associate Athletic Director Jason Cook.
So, what are the rules of using the 12th Man? A flag with a 12 on it is fine, because you can't trademark a number. But once you add a the "th" or the word "man," you could be in trouble.
"Just today I've received a couple of reports of local businesses in the Seattle region using promotions tied to the 12th Man, and that is certainly not part of our agreement," Cook said.
The university has even used mystery shoppers to catch people using the term improperly. They went after the Denver Broncos in 2012 when a man parachuted into the football stadium with a Broncos 12th Man flag.
Chris Johnson got frustrated by the hoops he had to jump through using 12th Man, so he trademarked the term "twelves."
"Every once and a while a Texas A&M fan will say, 'Hey look, we are the 12th Man, you are not the 12th Man, you stole that from us.' But they can't say that about twelves," he said. "If Texas A&M wanted to use it, they would have to ask me if they could."
While it isn't as valuable as the 12th Man trademark, Seahawks running back Marshawn Lynch does own the trademark for Beastmode. His agent said Lynch has earned six figures by licensing the term, with all the money going to Lynch's charity.