Actually all civilians, Mercs or not, had strict orders not to join the Poldavian side. That meant that the only civilians fighting along the pollies where undercover PsyOps, and even though I would like nothing better than to have them wear a special armband I doubt if they will agree to the idea. We tried to distinguish trustworthy civilians by turning the armbands white side up but PsyOps caught on to that in no time and did the same to their armbands.Then there's the civilians. All fine and well, but the mercenaries are sorta annoying, as you can't always tell who's currently on your side and who's not. In the end battle, there were mercs who were fighting for us and mercs who were against us, all of course wearing the same civilian armband. Yeah, pick your targets, don't shoot friendlies! My suggestion: civilian mercenaries wear the armband of the current faction they are fighting for. Maybe even with some insignia showing that they are mercs, like the letter "M" on the armband.
However, the Sixth Mercs, who made up almost half of the civilians, all wore co-ordinated uniforms (black top, OD trousers) as well as the Sixth Mercs insignia, so if anything we should be the easiest force of all to recognize.