I'd suggest using a graphic similar to the one at the top of this page, except don't use the M-60. You could use two rifles, say a flintlock and an M-14, maybe with a Colt SAA and a 1911 in the foreground. Under the graphic, you could put something like "All gun talk, All the time" (not neccesarly that phrase--just a suggestion).
Then, simply put "www.thefiringline.com" on the pocket (if it's a pocket tee) or over the left breast.
How's that sound?