I guess I'm not helping unify our movement much by making this suggestion, but-
I think if it were me, I would change "OC" to Exposed Carry and "CCW" to Concealed Carry. I have a couple of reasons for this. First- not everyone understands what OC and CCW mean. Second- I wholly support concealed carry- but coming from a strictly constitutional perspective, licensing concealed carry really isnt a second amendment rights issue. The license, being an infringement, is what the 2A was intended to inhibit.
I'm sure there are people going "Whaaaa?" to the suggestion that "CCW" is not a second amendment issue, but that need not be explained on the "Join or Die" image.