I had a bicycle stolen last December. It was parked in the hallway outside of my office, unlocked. Some lowlife grabbed it and ran out the back door with it. I had not registered it with the police but within an hour I had located the receipt from the LBS where I purchased the bike in 2002 and reported the loss complete with sn.
Three months after the theft I saw someone riding my bike. I flagged him down and we had a a conversation. He was not the one who stole the bike - we had a description of the thief - but claimed he got it from a "friend." I convinced him that the bike was mine; telling him that I had in my report to the police that I had included the sn was enough for him to surrender it to me.
I'm still looking for the Nishiki I had stolen in 1979.