rule of thumb: if you can see the livery, you are to close :)
9/10 times IFF is figuring out what those 5 by 5 black dots on the horizon mean.
and, if you are realy fancy get on TS and simply ask "hey guys, is someone in a Mig21 over maykop" or even more fancy ask the GCI, because even if someone teamkilled the awacs again he can still tell you if you are aiming at a Friendly or open sky.
so yea best IFF is Comunication and checking the players pool. if the enemy dont have any f86...you probably scaring the hell out of an Mig15 pilot right now, manouvering into his 6 o'clock :)