Microsoft does not have a copyright on the phrase "405th infantry/etc" so we are safe from an infringement standpoint.
Where we might get in trouble is if we use any permutation of "spartan, ODST, EVA (all the other helmet types), etc" basically anything that is in the game.
And to be on the safe side, I'd plaster "we are not in any way affiliated with microsoft, xbox, halo, etc" all over the site / threads where you are selling 405th shirts,
otherwise you might have microsoft on our behinds with the quickness.
^ I like your "area code" idea.
Spartan 919
