In California and many other states, that I know of and visit, if a business does not want legally armed private citizens to enter and do business then they have to post a sign that shows this. Most states even have designed the specific sign that must be posted.
If a business owner or manager asks me to leave I will but the whole idea of carrying a concealed weapon is for it not to be detected or displayed. That is the law as well and those who carry on a CCW all know about both of these laws.
Yes we are mandated by laws.
My guess is you are mandated by law to post a no guns sign if that is your general policy. But like I said, this appears to have been special circumstances prompted by a particular customer’s irrationality. It might have been better to explain to the malcontent that they were cops. Anyway, businesses usually reserve the right to refuse service for a panopoly of reasons. For instance, just be ause they post “no shoes, no shirts, no service” does not mean you can wear shoes and a shirt with no pants. I don’t see why they couldn’t ask the cops to come back without their guns or leave altogether just because there isn’t a sign.