Just for clarity, there's a lot to be said for just acting as if you own the property and depending on the details, there's a good chance you'll never have an issue in your lifetime (when I was looking at homes recently, one that I was seriously considering had much of its fenced in yard and paved driveway on city property and it had been that way for at least several decades with no reason to believe that that the situation would change any time in coming decades). However PA state law doesn't allow actual adverse possession (with transfer of title at the end of the process) with municipally owned property.