Read the paragraph of the bill (295) here: http://www.govtrack.us/congress/billtext.xpd?bill=h112-3011&version=ih&nid=t0%3Aih%3A449
Excerpt from the bill:
‘Whoever, except with the written permission of the Assistant Secretary for Transportation Security (or the Director of the Federal Air Marshal Service for issues involving the Federal Air Marshal Service), knowingly uses the words ‘Transportation Security Administration’, ‘United States Transportation Security Administration’, ‘Federal Air Marshal Service’, ‘United States Federal Air Marshal Service’, ‘Federal Air Marshals’, the initials ‘T.S.A.’, ‘F.A.M.S.’, ‘F.A.M.’, or any colorable imitation of such words or initials, or the likeness of a Transportation Security Administration or Federal Air Marshal Service badge, logo, or insignia on any item of apparel, in connection with any advertisement, circular, book, pamphlet, software, or other publication, or with any play, motion picture, broadcast, telecast, or other production, in a matter that is reasonably calculated to convey the impression that the wearer of the item of apparel is acting pursuant to the legal authority of the Transportation Security Administration or Federal Air Marshal Service, or to convey the impression that such advertisement, circular, book, pamphlet, software, or other publication, or such play, motion picture, broadcast, telecast, or other production, is approved, endorsed, or authorized by the Transportation Security Administration or Federal Air Marshal Service;’.
Now, this doesn't necessarily on free speech at first glance. However, I could easily see why someone that is a bit...overzealous...might think they can get away with trying to disallow any parody. Think of the SNL skit about the TSA.