I seem to remember somebody making one that flipped down.
You can't hit the base auto/hobby shop, and scrounge a piece of stainless sheet metal or something, just bend it, and drill a hole or something in it....use one of the fairing plastic screws to attach it?
Or one of the bolts on the forks? I can't remember the correct display position. Back when I was in the Army, they didn't care where we put the stickers on our Model T's.
Maybe look at some of the bikes parked on base for ideas?
It wouldn't take much....
I think there may be a commercial product, also...I think I've seen something for Toll passes, or something.