Whether or not a retailer or other merchant places restrictions on a particular activity is a private property issue. We, as consumers then can make a choice of whether or not we will spend money with that business, and have the freedom to tell others about it.
What has been emphasized here before in other posts, is thatbusinesses placing an irrational ban on lawful firearms owners, is alsomaking a declaration to all the criminals that none of the people who patronize the establishment are armed. I think Ive even seen a sign depicting an unarmed man being mugged, with thewarning "No Firearms, Crime Zone".
Here in California, I have yet to encounter a sign specifically denying the carrying of firearms, lawful or otherwise. The only place I would heed such a sign would be at the county courthouse or other official building.