This entry provides the one- or two-character alphanumeric code indicating the nationality of civil aircraft. Article 20 of the Convention on International Civil Aviation (Chicago Convention), signed in 1944, requires that all aircraft engaged in international air navigation bear appropriate nationality marks. The aircraft registration number consists of two parts: a prefix consisting of a one- or two-character alphanumeric code indicating nationality and a registration suffix of one to five characters for the specific aircraft. The prefix codes are based upon radio call-signs allocated by the International Telecommunications Union (ITU) to each country. Since 1947, the International Civil Aviation Organization (ICAO) has managed code standards and their allocation.