The serial number is a string of numbers and letters that identifies your watch. It's usually located on the back of the case or dial, but it can also be stamped on an inside part of the watch.
If you have a vintage watch, you may need to find its serial number to get information about it.
You can still find out what model and year it was made using information from other resources, such as an entry in an encyclopedia or an advertisement for a particular watch model.
Vintage watches are often more valuable than modern ones—and more difficult to find! This is because they were produced in smaller numbers and often only sold through specialty shops that specialized in only those kinds of timepieces.
If your watch doesn't have its original box or papers with it, but does appear relatively new compared to some of its peers (at least compared with other pieces in similar condition), then chances are good that there's something wrong with this piece—it could be damaged or broken down into parts (which would make finding out where each part went even harder).
You'll find your watch's serial number on the back of the case. It may be stamped on, or engraved into, this part of the watch's body. If there are no numbers on your case back and you can't see them in any other way, then you'll need to open up your watch and look inside.