Pawn shops routinely check watches for serial numbers. They record this information on the watches' pawn tickets and use them to help police locate stolen items, if necessary.
Pawn shop owners keep a very close record of their inventory, especially when it comes to valuables like watches. When someone pawns a item, the pawn shop always checks to see if it has a serial number on it, and if it does, the staff write it down on the item's pawn ticket. This is a way for the pawn shop to make sure tit has the most thorough record of an item possible, including all pertinent and available information about that item.
If the police are searching for a particular stolen watch, they may ask a pawn shop to check the serial numbers on the watches to see if any of them match the stolen one. This is another reason why pawn shops check watches for serial numbers.
Since most watches come with serial numbers, pawn shops check every watch they receive to try to locate one. Keeping records of these numbers also helps the pawn shop in the event that any of its inventory gets stolen. From its records, it can provide the specific serial numbers for any missing items to the police to try to track them down.