I don’t think I’ve ever seen a ruling on this, but...
wouldn’t you think that a “no guns/weapons” policy would be an inherent requirement for providing security to the patrons and employees?
IE, if someone gets hurt because of the inability to defend themselves due to the policy of the business owner, and his failure to provide security, then he should be liable for any harm that comes to the patrons or employees.
I don’t think they can be healed libel for another persons illegal action.
That being said, public buildings in my state cannot put up a no guns sign unless they have a way to screen for guns and have an armed guard to protect the occupants. Our public library is spending a fortune to keep legal carriers from legally carrying.