I would think you should be able to bring the firearm into the police department of one of your Police Officer friends and have them inspect the firearm and run the serial number. If it's not stolen they will probably write and incident report that you brought in a firearm to have the serial number checked, Officer XXX personally inspected the firearm and ran the serial number and it was not reported in the system, end of report. If it's stolen however they will take it, ask you how you acquired it and open an investigation in an attempt to solve the case. If it is stolen I'm sure you would want to have the gun out of your hands and with this post as proof it would be easy to back up your story that you found the gun. That's just what I would do. Definitely don't just turn the gun in as found property though.