In this case, that tautology also means violating the wishes of the person owning or renting the property. It can be (and has been) argued that liberty is based on the right to control one's property.
There might be cases in which I must be in a certain place, and that my safety is definitely compromised, where I would see violating the rights of a property holder. But that would have to be a very specific and grave situation, and a gun show doesn't meet that definition.
Whether or not the signs have weight, carrying somewhere against the wishes of the property owner is something of a moral compromise.