Traffic Lights, Signs and Controls: Are Stop Signs Enforceable in Privately Owned Parking Lots

My question involves a traffic ticket from the state of: PA



I have been wondering about this for a while and today I googled it and spent some time looking for answers, just wondering what you guys think, also I read a few things on the net that said these signs are not enforceable, that also makes me wonder if handicap areas in private lots are enforceable by police. so whats the deal,, what is and is not enforceable in private areas/parking lots ?

Traffic Lights, Signs and Controls: Are Stop Signs Enforceable in Privately Owned Parking Lots