IDs are both inRP and ooRP item. InRP they serve as identification of to what faction ship belongs. All the rules and restrictions are of course ooRP stuff. Formally it should be marked with // but I think everybody understand that ZOI restrictions text is ooRP.
Edit: What you propose will open lot of possible loopholes and abuses (and this is exactly why the IDs were made visible inRP again). Some factions will be basically allowed to fly "unidentifiable ships", because without tag and with generic IFF, ships will become unidentifiable and there is no way how you can "roleplay" around it when you can´t arrest and interrogate the pilot unless he himself agree with it.