Practice Relating to Rule 63. Use of Flags or Military Emblems, Insignia or Uniforms of Neutral or Other States Not Party to the Conflict
Sweden’s IHL Manual (1991) considers that the “prohibition of improper use of … emblems of nationality”, as contained in Article 39 of the 1977 Additional Protocol I, is part of customary international law.
The manual also notes that, during the CDDH:
There was a consensus in favour of introducing a rule forbidding this type of abuse on the part of belligerents. It should be noted that Article 39:1 [of the 1977 Additional Protocol I] prohibits any form of use in armed conflict. The rule relates not only to the uniforms etc. of neutral states, but also to those belonging to states that – without being neutral – are not parties to the conflict. By this are meant states that have the status of non-belligerents.