It depends on the laws in your state.
In mine, it's considered criminal trespass, a class A misdemeanor. That's enough to revoke your CHL.
The law has been clarified to make effective notice for a "no guns" policy be very clear. A compliant sign has to be about 2 feet by 2 feet, with specific wording in English and Spanish. Or, they can provide printed notice -- handing it out to you as you enter.
Which state is that, if you don’t mind me asking?