ICRC databases on international humanitarian law
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1949 Conventions and Additional Protocols, and their Commentaries
Historical Treaties and Documents
Rules concerning the Control of Wireless Telegraphy in Time of War and Air Warfare. Drafted by a Commission of Jurists at the Hague, December 1922 - February 1923.
Part II: Rules of Air Warfare#Chapter IV: Hostilities. - Art. 19.
Art. 19. The use of false exterior marks is forbidden.