Bikes have a unique serial number that are engraved on the bike frames, usually under the bottom brackets where the pedals meet. Closely examine all of the bike components -- the serial number could be engraved in one of several different places.
Refer to the bike manufacturer’s website for possible further information on the bike’s serial number. After a new bike purchase, write down the serial number, make and model of the bike in a safe location in case of an emergency. If the bike does not have a serial number, it's possible to engrave a driver’s license number on the bike to create its own identifier. A serial number or other numeric identifier makes it possible to register the bike at a local police station and offers a better chance of recovery in the event that the bike is stolen.