Tresspass law in Pa

What is the name of your state (only U.S. law)?Pennsylvania: We have a neighbor (new withing the last 3 years) that owns property three parcels over. The two parcels in between have never been posted and have been open to hunting which we have done on these properties for many years. Suddenly this new neighbor has "taken over" and posted these properties and is claiming he's in charge of them. Both properties are owned by out of state residents who do not visit and do not have any improvements on the properties. I have written to these out of state residents and do not get any response. Normally I would assume that maybe this new neighbor did obtain the administrative rights to these properties but I have caught him in lies before and he seems to be a "bully". I don't want any trouble with the law so I'm concerned if I have to retrieve game on these lands (shot on our property) that I can be procecuted for tresspass. My question is, does this new neighbor have to present some type of written form to assert his administrative rights and if not can I ignore him?

You don't get a say in this. If the owners of the parcels don't want to press their rights, you can not do it on your own. The neighbors do not have to prove anything to you.

Of course, if they're not pressing their rights with respect to his signs, they're not likely to press them with regard to your trespassing. The neighbor can't have you charged with trespassing, only the owner.

Why not renew efforts to contact the owners and ask them for permission? Get it in writing . . . better hunting for you if it's posted against all others anyway.

You could possibly be guilty of "Agricultural trespass" or possibly "defiant trespass" if you knowingly enter property posted in a proper manner, or ordered not to enter by the "owner of the lands or other authorized person." (Criminal trespass - 18 Pa. Cons Stat. 3503).
The question then becomes whether the person is authorized to give such an order. I would say that you should ask him for some document showing his authority, and if he refuses, then you cannot be "knowingly" ignoring an authorized order.
The no trespassing signs are another matter. It is possible that the signs must contain the name and phone number of the owner, or some other regulation to make them "proper", and perhaps you should research whether the signs are "properly" posted.
PA also has a Code (137b.64) that allows entry into farm lands if they are enrolled as agricultural reserve land. That is usually done so as to get a tax break on farm land. There are some rules that apply, and the landowner may prohibit hunting. You could probably find out from the Town tax office if any of the properties receive a tax reduction for "reserve land".
I'd keep trying to contact the actual owner.

Maybe the next question to ask is if the out of state owners have ever known and/or given permission for you to hunt on their land?