18 U.S. Code § 700 - Desecration of the flag of the United States; penalties. Whoever knowingly mutilates, defaces, physically defiles, burns, maintains on the floor or ground, or tramples upon any flag of the United States shall be fined under this title or imprisoned for not more than one year, or both.
I'm pretty sure that would fall under the physical defile, but they would counter with 1st amendment.
Basically any negative action with it, can be punished, but one could claim that's not a negative action but taking pride in it.
