One of the results of the Convention on International Civil Aviation, which established the ICAO , was new rules regarding aircraft registration. If you pay close attention, you'll notice that all aircraft registered in the same country begin with the same characters. Some of them seem very straightforward; for example, the aircraft registration prefix for Canada is "C," Japan uses "JA," and Germany uses "D.
" According to ICAO , "Annex 7 Aircraft Nationality and Registration Marks adopted by the International Civil Aviation Organization (ICAO) provides Standards & Recommended Practices for the display of appropriate aircraft nationality marks, common marks and registration marks which have been determined to comply with Articles 17 to 21 of the Chicago Convention." The classification of different types of aircraft in Annex 7 Lighter-than-air aircraft Any aircraft supported chiefly by its buoyancy in the air. It includes: Non-power-driven balloons (free balloons, and captive or tethered balloons), and Power-driven airships.
Heavier-than-air Any aircraft derives its lift in flight chiefly from aerodynamic forces. It includes: Non-power-driven aircraft (gliders and kites), and Power-driven aircraft (airplanes, rotorcrafts such as gyroplanes, helicopters, and ornithopters). There are only 26 letters in the English alphabet, so some countries had to get creative.
However, some prefixes are somewhat obscure, like Singapore's registration prefix "9V," Israel with "4X," or the Nether.