Treaties, States Parties and Commentaries
Treaties and Documents
Geneva Conventions of 1949 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 I: Domain of application: classification and marks. - Art. 6.
Art. 6. Aircraft not contemplated in Articles 3
and considered as private aircraft shall carry such papers and exterior marks as are required by the rules in force in their own country. Such marks must indicate their nationality and their character.