If you want to identify which Peugeot bike model belongs to, locate its serial number on the underside of the bike's lower frame. We can begin to identify Peugeot bicycle models from the 1920s. The leading bike model introduced in this decade was the Peugeot P-10. Peugeot used six digits to mark its bikes released in the 1950s and 1960s, some even having seven digits in the late 1970s. As for 1980s bicycles, they have eight digits and an alphanumeric prefix in the serial number. Models introduced in the 50s had PC-10, PH-10, and PLX-10 in their serial numbers.