You can only be trespassed if you refuse to leave when asked, if I understand right. Just because a business has a "No guns" sign on the door doesnt mean you can be arrested for entering with a gun.
Depends on the wording of the sign: "Anyone found in possession of a firearm on these premises without the permission of the owner shall be treated as a trespasser." would be hard to argue against. "No guns allowed" is a notice, but not a binding one under the law.
IANAL. TINLA.
^^^^^^
This.