That's just not true from a legal standpoint.
Starbucks Coffee can't use "Have it your way" by arguing that Burger King's trademark only applies to hamburgers.
If you want to argue that all trademarks should be abolished, fine. That's a different debate. But you can't argue that some should be respected and some shouldn't depending on your allegiance to a particular football team.
OK, well I'm not an intellectual property lawyer.
But, for instance, say the Seahawks sell a Jersey in their proshop that has the number 12 on it.
Are the Seahawks the only team in the NFL that have Jerseys with 12 on it? Of course not.
So unless A&M is gonna insist that the entire NFL and all collegiate football retire the number 12, then they CAN'T say that they have absolute, exclusive rights to it.
So I don't see them prevailing in court.
Trademarks have to be vigorously defended, however, or they fall into the public domain. That is why corporations have to play hardball with mom and pop stores, high schools and charities when their trademarked slogan is borrowed by someone else.
Coca Cola has tried to do this with the trademarked term "Coke". In the south and other places, "Coke" has become a generic term for all soft drinks, but (AFIK) Coca Cola still defends any usage of the term for commerical or advertising reasons.
The term 12th man is very generic and has been used by every high school and college in America - maybe not to the level that A&M has used it, but still it is very commonplace. As far as I know, A&M has not vigorously defended this term when high schools and colleges have used it. If they haven't then a court challenge by them would probably result in them losing the trademark altogether.
Something has really happened to A&M the last few years. I used to really like them, but lately they seem to exhibiting really bizarre behavior.