How did aircraft nationality markings (N numbers) begin?
In 1919, an international treaty assigned “N” as the designator for U.S. aircraft. The United States did not sign this agreement, however, so use of the “N” did not become compulsory then. In December 1926, the first U.S. Air Commerce Regulations set up a system of licensing and identification marking for aircraft. In March 1927, amendments to those regulations mandated that U.S. aircraft engaged in foreign air commerce display the letter “N” at the beginning of its identification markings. Today, all aircraft registered in the United States must carry the “N” marking regardless of where they operate.
