Swattie,
Careful. If you are on another's property, legally, illegally, invited, or whatever, you are defined as a trespasser. It's just that trespassing itself isn't a crime in PA. Illegal trespassing is a crime.
A landowner could also assume that said trespasser is posing harm to him personally and his property.
I don't see why, but sure, why not? But if the trespasser is legally there, then the landowner can in no way harm or threaten the trespasser. All he can do is tell him to leave. If the trespasser refuses, then the landowner can threaten prosecution.
Going the other way, it's common for many would be hunters and fisherman to claim a bunch of B.S. about "proper" posting. It has to be signed. They have to be spaced every ___ feet. etc. etc. etc. Therefore this signage is invalid and I can hunt and fish here.
It's all B.S.
If you saw a sign. Even a SINGLE, unsigned one. Then you saw it. You've been informed. It's that simple. You are to assume the entire property is posted. And if the boundaries aren't clearly marked, it's on you to look up where the property boundaries are and stay off the entire thing. If you want access, it's on you to find out who the owner is and ask.
The test is whether you were informed that you are not welcome. If no, you are free to go on that land. If yes, then you're not.
My biggest complaint is that many landowners have specific instructions, but just put up the "no trespassing sign". For instance, I know landowners who are happy to have people access their property by foot, but they don't want people to drive on their lane, for instance. But instead of putting up a sign that says "fishing and hunting permitted, please don't drive on my lane", they just have a "no trespassing" sign on a tree by the lane. Legally that renders the entire property of limits to any access at all. If a landowner merely has rules about access, then post the rules.