Texas A&M has sued the Indianapolis Colts for infringing on its trademark of "12th Man."

At a board of regents meeting Thursday, school chancellor John Sharp revealed that Texas A&M filed suit in U.S. District Court in Houston after repeated attempts to stop the Colts from using its registered trademark were unsuccessful.

The suit, filed Thursday, alleges that the school first contacted the Colts in 2006 about the use of the phrase inside their stadium and sent a cease-and-desist letter, which the school says fell on deaf ears.

The Colts retired the "12th Man" in their ring of honor in 2008, and according to the suit, were again warned by A&M that the team was infringing on a mark that the school owned.

The tipping point came in July, when in an email advertisement to sell tickets, the Colts encouraged fans to "Join The 12th Man." School officials discovered the infringement when a person in College Station, home of Texas A&M, received the email.

In addition, the Colts have used "12th Man" to sell merchandise and have been honoring fans with a "12th Man award" during games in which the honoree receives a Colts jersey with "12th" on the front.

"Texas A&M University is the Home of the 12th Man which has brought our fan base national renown," school president Michael K. Young said in a statement. "We would prefer not to file lawsuits to protect our trademarks. However, when our intellectual property, especially the 12th Man mark which is so important to our students and former students, is used without our permission after repeated attempts to engage on the matter, we are left with no choice."

Chancellor John Sharp says Texas A&M has made repeated attempts to ask the Colts to no longer use the "12th Man" trademark. AP Photo/David J. Phillip

"We're aware of the media reports of the Texas A&M lawsuit but we've not yet had an opportunity to review the actual complaint," said Colts spokesman Avis Roper. "We'll make a statement after we've actually been served and had an opportunity to evaluate the allegations."

This is the second time the Aggies have filed suit to protect their "12th Man" trademark. In 2006, they filed a lawsuit against the Seattle Seahawks for using the phrase without being authorized. The result was a settlement that allowed the Seahawks to license the phrase for $5,000 a year, but did not include the right to sell merchandise with the phrase on it. Instead, the Seahawks sold No. 12 jerseys with the nameplate "FAN" on the back that became very popular.

The Seahawks renewed their "12th Man" license for the past 10 years through June 2016. It is not clear if they will continue to do so.

Football Northwest LLC, the holding company of Seahawks owner Paul Allen, is currently the owner of five registered trademarks to "12," two to "The 12s," two to "The Spirit Of 12" and one to "We Are 12."

One other NFL team, the Buffalo Bills, has a license from Texas A&M for "12th Man," but it's only for extremely limited use inside the stadium.

Texas A&M's use of the "12th Man" goes back to 1922, when a student named E. King Gill came out of the stands and got in uniform ready to play if called into action. It's why Aggies fans stand throughout games, a symbol of the willing sacrifice of Gill and the role they play in the game.

Texas A&M has four registered trademarks to "12th Man," with the first filed in 1990.