It really is a good idea. If people want to make something for themselves, they are more than welcome to I would suspect. Just have the site text on the shirt somewhere so that you are identifying a gaming unit and not saying that you are part of a military unit. I can go anywhere online and get Navy shirts that have ESWS/Ratings on it without it being a big deal.
On a second note, if you are ever wanting to get into the biker community, be EXTREMELY careful with wearing shirts with diamonds with 1's in it (as depicted below). You may be mistaken for a 1%er and trouble would ensue. (Just a helpful tip.)