Oh FFSIf you're a Costco member, membership rules say you can't. There's no need for a sign or for them to explicitly stop and ask you every time. It's part of the membership agreement you agreed to. Penalty for doing it could be revoking membership and potential ban from Costco. They're a club, not public. If you're going into Costco and not a member... well, there's not much of a point to that is there?