Any civil aircraft, whether it is rented or owned, must be registered with the relevant national aviation authority, and a tail number (or N number) is a unique identification number painted on the tail of the aircraft similar to a license plate on a vehicle.
Just like on a vehicle, each tail number is unique. But, some countries allow it to be re-used if the aircraft is destroyed, sold or retired. And a different one can be assigned to the same aircraft should its ownership or registration law change.
In the United States, N numbers may not start with a zero after the country’s prefix, and will not include the letters “I” and “O” since they are ,visually, very similar to the numbers “one” and “zero”.
Each country has different combinations of alphanumeric characters in the form of prefixes and suffixes. For example, a US tail number starts with the letter “N”, whereas the letter “G” is used for airplane registered in the UK, “JA” for Japan, “D” for Deutschland, ”C for Canada and “B” for China.
An aircraft identification number must be displayed conspicuously on the aircraft, and some countries require it to be engraved on a permanent fireproof piece that’s part of the aircraft’s fuselage to be identified in the event of a fire or a plane crash.
An infographic about aircraft registration numbers – By the Avijet’s team.