Related Rule
Practice Relating to Rule 63. Use of Flags or Military Emblems, Insignia or Uniforms of Neutral or Other States Not Party to the Conflict
Belgium’s Teaching Manual for Officers (1994) stipulates that the use of flags, symbols, insignia and uniforms of neutral or other States not parties to the conflict is prohibited “in all circumstances”. 
Belgium, Droit de la Guerre, Manuel d’Instruction pour Officiers, Etat-Major Général, Division Opérations, 1994, Part I, Title II, p. 34.