It is an IFF HUD element, but it only makes sense to impliment in certain situations. When Accepting a mission to go support Company personnel, it is beleivable to assume that said company has some sort of IFF system they can give you guest access to. But, however, if you are addressing a hostage/hijack situation, it would make sense that there would be a bit of confusion as to who is who.
~Then again, I play a lot of Squad and Arma where target identification is an intentional gameplay challenge at times~