Rolex began making watches early in the 20th century and was a pioneer in changing over from pocket watches to the wristwatch. It is estimated that Rolex produces between 700,000 and 800,000 watches per year and every watch is provided with a serial number and a registration number. Non-authentic Rolex watches do not contain valid serial or registration numbers. Contact an authorised Rolex retailer or jeweller with questions about how to properly identify an individual Rolex watch.
Remove the watch band and look between the lugs (links) at the 6 o'clock position. This is the serial number. If you have difficulty removing the watch band, have a jeweller assist you. Record this number for your records.
Look between the lugs at the 12 o'clock position. This is the registration number. Record this number for your records.
Check the production date of the Rolex watch, if possible. Rolex watches made before the 1940s have the serial number stamped on the case back.
Learn more about Rolex watches through history, as the watches have changed over the decades. This will help you identify individual Rolex types, styles and historical information. One good reference is the book "The Rolex Report: An Unauthorized Reference Book For The Rolex Enthusiast" by John Brozek.
To identify a Rolex as belonging to a specific individual, have an authorised jeweller engrave something personal on the case back.