Using Navy ID don't help in undercover RPing and stuff in my opinion.When people see Kempeitai or MND or LSF ID they can manage to get that you trying to fly undercover.
With GRN ID it's most likely "LOOK GRN! ENGAGING!"
The Gallic Royal Navy (GRN|) has a separate branch called the "DOS". (D'operations speciales or something, this spelling is wrong I tell you) which has roleplay stories and ingame characters. We don't need a separates ID or IFF for it. Works fine right now, don't over complicate it.