Are you a 12th man?

 I am a Seahawks fan. They give partial credit of their wins to their fans, known as the "12th man", now known as 12's -  *see update below 

The following information is from this article on Wikipedia - 
(12th man (football) http://en.wikipedia.org/wiki/12th_man_%28football%29

Effects
The effects of the "12th man" vary widely, but can be put in two categories. The first is simply psychological, the effect of showing the home team that they are appreciated, and showing the away team that they are somewhat unwelcome. The second directly relates to the deafening effects of a loud crowd.
In American football, fans are most incited by physical play, especially good plays made by the defense. Additionally, the home team can derive energy from the loud noise of their fans; former American football players have described the feeling of their adrenaline pumping after hearing the fans yell, which is "like you have a reserve energy tank."
The noise of the crowd can have a significant impact on the players on the field. In American football, an extremely loud crowd can prevent the offensive linemen from hearing the snap count. This can have the effect of making the player slower to react when the ball is snapped, and his eventual response may be weaker than normal because each play is begun "with some indecision and doubt." The noise can also prevent players from hearing audibles and can make it difficult for the team's offense to coordinate plays in the huddle. The effect of the noise can often be measured in mistakes, such as false start penalties.
Coaches can take steps to minimize the effect of the crowd noise on their teams. Some American football teams bring large speakers to their practice fields and broadcast loud noises such as jet engines to prepare their teams for the anticipated noise level. Crowd noise tends to diminish after a long lull in play, such as a pause for instant replay. Former NFL player Brian Baldinger speculates that some coaches draw out reviews as part of a coaching strategy to quiet the crowd for their next play.
The New York Giants allegedly asked the NFL to intervene in 2006 when they played the Seattle Seahawks. In their 2005 match up at Qwest field, the Giants incurred 11 false start penalties due to the crowd noise. For the 2006 rematch between the two teams, the NFL sent observers to verify that the Seahawks were not artificially enhancing the noise level. This has caused 2.83 false starts per game, which is the highest in the NFL since 2005. The noise level at Qwest field has been measured at 112 dB.

Use in American football
The term has been used by various American football teams including the NFL's, Seattle Seahawks, Green Bay Packers, Buffalo Bills, Denver Bronco's, Washington Redskins, Indianapolis Colts, and Chicago Bears in marketing practices in reference to their supporters, though many stopped using the term "12th man" at the request of Texas A&M (the Bears currently use the phrase "4th Phase"). The Seattle Seahawks continue to use the phrase, having settled with Texas A&M out of court after a trademark lawsuit filed by Texas A&M.
The Seattle Seahawks retired the number 12 jersey on December 15, 1984. The tradition of raising a 12th man stadium flag before kickoff, by either season ticket holders or celebrities, began on October 12, 2003.
In 1992, the Buffalo Bills honored their 12th man by inducting them into the Buffalo Bills Wall of Fame inside Ralph Wilson Stadium. They were inducted because of their loyal support during the team's early 90's Super Bowl runs.
The Indianapolis Colts honored their 12th man by inducting them into the Indianapolis Colts Ring of Honor in 2007.

Texas A&M trademark issues and Seattle Seahawks lawsuit
*as of August 2015 we are no longer the 12th man, but we are now the 12's. It looks like Texas A&M got their way (http://www.foxsports.com/nfl/story/seattle-seahawks-12th-man-controversy-texas-am-081515). The term "12th Man" is used non-exclusively to represent the Texas Aggie fans. Intellectual property laws recognize certain common law uses in trademark dispute. In spite of the fact the term originated with another university, an official registration of the mark was filed by Texas A&M (U.S. Reg. No. 1948306) in December 1989 and the application was approved by the United States Patent and Trademark Office in September, 1990. According to statements made by Texas A&M officials, they sent requests to stop using the phrase to the Seattle Seahawks (2004, 2005), Buffalo Bills (undated), and the Chicago Bears (undated). Both the Bills and the Bears responded to the requests stating they would no longer use the phrase, however the Seahawks did not respond to the request.
In January 2006, Texas A&M filed suit against the Seattle Seahawks to protect the trademark and in May 2006, the dispute was settled out of court. In the agreement, Texas A&M licensed the Seahawks to continue using the phrase "12th Man" in exchange for financial compensation along with public acknowledgement by the NFL franchise as to Texas A&M's ownership of the phrase.

^{GO SEAHAWKS}

^{BIGGER, FASTER, STRONGER, LOUDER!!!!}