Actually, me and friend were just looking into this because he wanted to get his stickers off the forks as well. Another friend of mine, Moose, his dad builds custom bikes, so we asked him figuring he would have the best idea of what is street legal (I'm from PA too by the way).
According to the law, the inspection sticker has to be mounted to something that is considered "semi-permanent" on the bike. Meaning that technically a bolt on plate is not legal - however if you run a single pop rivet through that same plate along with the bolts, then it's legal.
Now having said that, he also freely admitted that this is one of those PA laws that tends to get overlooked unless the cop just read it in his manual and he's feeling like a dick.