When we asked the manager in Costco about their policy, he handed us the policy statement from their website that says you can NOT carry in Costco. When we informed us that they should have a sign on their door stating such, they said they don't have to do that to be able to enforce their policy BECAUSE they are a club store and, therefore, are not a place of "'public accommodation' within the meaning of civil rights laws. The definition of 'public accommodation' does not include a bona fide private club or other establishment that is not in fact open to the public".
They obviously have lawyers too! Costco, in my opinion, is trying to have it both ways here. They have a policy, but REFUSE to post such notification on the front of the store because they KNOW that in this state it would cost them business. I am dumping my Costco membership and joining Sam's Club.