I think you need to look up the trespassing laws. I have never been told I can not enter the establishment and unless they have told me to leave or not welcome in that place of business.
And if I am concealed properly they won't know I have it unless I need to use it. And before they call the police it would behoove them to verify who the individual is as they could be somebody that is an exception such as a LEO.
There has already been a few lengthy debates about the gun buster signs and the legal consequences on this forum. I have asked actual police officers in my city and the general consensus is the sign is the only warning you are entitled to. The owner/manager does not have to ask you to leave. And if he calls the cops, most officers will just ask you to leave but they may arrest you if they are in the mood. What they arrest you for depends on how you handle the encounter. Every officer is different and not all of them like handguns in public. Business owners are allowed to restrict guns on their property its in the SDA.
Just don't get caught and if you do be polite and leave immediately.