A traffic stop is not always a violation of the law. That being said, I believe it is reasonable to assume that a law abiding citizen with no intent to cause harm would not violate a posted sign. Thus, it is reasonable IMO for the security force to assume a threat, if it were my house, depending on who you were, I might.
It's not your house. It's a business open to the public. It is, as you say, a striking difference.
You make a lot of assumptions that you haven't been able to back up with ONE case to support your theory.
I'm a lawful gun owner & violate stupid no guns signs at businesses all the time. It does not make me a threat, imminent or otherwise. I know with a very high level of confidence that there are many others here who do the same. They have stated as much. Are we now suddenly all threats?