most buisness owners dont put much thought into the idea when they put up their signs, The more people bring this to their attention the more will take the signs down. Even an anti-gun friend of mine admitted to me that gun free zones scare him, and has actually lightened his stand on the subject... (at least in this regard).
This isnt about whether you or I want to pack heat when shopping, its really a public safety issue. Present it in this way and the light will turn on. There isnt even a need to make it about gun rights or even bring up that you carry....