In my state OC is legal, and signs on private businesses hold no legal weight.
It's private property, if they do not want weapons in their store, they are legally allowed to deny that. They are allowed to deny service to anyone they want. And if there was a sign that said no yellow shirts or you will be kicked out, guess what, find a blue shirt. That's like saying that people who do not like to wear shirts and shoes should stand up and protest because of the signs that say "No Shirt, No Shoes, No Service." They are within their legal rights to not allow you to have a weapon in the store. So if you come over to my house and you are open carrying, I have to let you into my home? or to my garage sale? It's private property either way, not public property.