Accoring to handgunlaw.us. they changed their PA page in regards to no gun signs having the force of law from ???? to NO.
Don't have a legal cite. They don't list one.
IANAL
Do “No Gun Signs” Have the Force of Law?
“NO”
“Handgunlaw.us highly recommends that you not enter a place that is posted "No Firearms" no matter what the state laws read/mean on signage. We recommend you print out the No Guns = No Money Cards and give one to the owner of the establishment that has the signage." As responsible gun owners and upholders of the 2nd Amendment we should also honor the rights of property owners to control their own property even if we disagree with them.”
“No Firearm” signs in Pennsylvania have no force of law unless they are posted on property that is specifically mentioned in State Law as being off limits to those with a Permit/License to Carry. If you are in a place not specifically mentioned in the law that is posted and they ask you to leave, you must leave. If you refuse to leave then you are breaking the law and can be charged. Even if the property is not posted and you are asked to leave you must leave. Always be aware of the possibility that responding Police Officers who may have been called without your knowledge and may not know the laws on trespass etc. could arrest you even if you are within the law.
Don't have a legal cite. They don't list one.
IANAL