Could be he was applying the military concept "under cover / under arms" to CCW. 
http://en.wikipedia.org/wiki/Cover_(military)
http://en.wikipedia.org/wiki/Under_arms
____
Unlikely, since that NRA hat is not military issue. Could be he just liked his hat, which is his privilege.
The poll worker was wrong. Clearly, an NRA partisan will robotically support any candidate who toadies to NRA intimidation, but that factor does not give the poll worker the right to invoke a dress code against this gun enthusiast.
+++
Unlikely in my example because its sort of an inside joke between those who know and have experienced military protocol. LIke a couple of vets standing inside in line to vote with their hats in their hands and see this guy with a hat on inside and say smiling with a knowing nod to one another "I'll bet he's carrying" and civvies standing within earshot of their conversation would not having a clue as to what they were joking about. Probably wouldn't see it a joke at all.
Like here
Oh well. 