With 4 acres and no trespassing signs, you will be fine. Also, it's illegal to drink n hunt and respectable hunters don't violate private property. Hunters tend to have "their spots" that they return to each season rather than roaming around endlessly. Although the roaming tactic does seem to be more common among the ones who come up with their buddies from NJ for guys weekend with guns.
If you buy 10 acres or more, and participate in the clean and green program to save on your taxes, however, you cannot prohibit people from walking across your land etc, other than the one-acre related to your home. It's technically even illegal to post your property if you participate in clean and green. Safety Zone signs are a better tactic, but your vehicle will one day thank you for being more receptive to hunting after you've spent enough time in PA and dealing with head-on collisions.