Opposing players who play in Seattle are well aware of what "the 12th man" truly means. Dubbing their fans as “the 12th man” (the 12th member of their team) is primarily due to Seattle's raucous fans’ contribution in their victories. This is because the Seahawks fans are known for their rambunctious nature. For instance, when Seahawks play at home, the fans are known to make ear piercing noise. No, make that world record noise, 136.6 decibels worth to be exact. This is enough to temporarily deafen opposing players, often confusing them on offense due to their lack of being able to hear any play calls or audibles, and consequently causing opposing teams to implode and lose games.
As last year’s defending Super Bowl champs, the Seahawks simply started using the number “12” rather than “the 12th man.” This was primarily because Texas A&M, a well-known college football university filed a lawsuit against the Seahawks for using their mark “the 12th man”. Consequently, both parties reached a settlement, causing the Seahawks to enter into a license agreement, which would pay the university a montly amount for the Seahawks to use “the 12th man mark."
After all this, the Seahawks have now filed the number “12” (yes, the one after the number 11) for federal registration with the Trademark Office. As one reporter from Seattle Times writes
“The team has gone further, filing two trademark applications for the number “12” in general. The Trademark Office has turned down one application due to a previous trademark for a NASCAR team. Another was refused due to a previous trademark for a hotel. In the meantime, the team has also pursued trademark of “12” in the team’s jersey font, which has some similarities to other NFL jerseys, such as the “12” worn by New England Patriots quarterback Tom Brady.”
However, on another note, the Seahawks have been successful in trademarking the phrase “Legion of Boom”, referring to their stingy secondary defense. They have also filed for federal registration for the mark “Boom.” However, as of now, this process is facing heavy opposition and has not been approved by the Trademark Office.