Inspired by yet another thread with a LEO 'run the serial number' in it.

Can someone object to the 'run the serial numbers' and if so what would happen? I had a local speedtrap cop 'run the serial numbers' on my pistol once years ago. I told him it was not purchased in PA and wouldn't show up, but he ran it anyway.

Since PA 'doesn't have' a firearms registry, what are they running it against?