There are several ways to get a good idea on who is what and it starts at the briefing screen. Take a look at the maps a few minutes before take-off and see what is out there. You can take a look at the ATO as well. Pay attention to AC operating beyond the flot as this is where enemy AC will be coming from.

You can also check out which airbases are operating AC for additional info. What you are after is to build up Situational Awareness. We try to do this with as much data as we can get our hands on.

So once you've checked out the map, the next thing you can do is use your wingmen. You can tell them to attack your target - if it's a friendly they'll tell you (though I consider this to be a bit of a cheat).

Migs have dirty engines, they will leave a black trail behind them which is noticable from many miles out when using your NVG's. Again, this is a bit of a cheat as the real things probably wouldn't allow this. One point here, friendly AC that are damaged emit black smoke too.

Your RWR is probably your best bet. If it has a mig at your 12 and you have a radar contact at your 12, there's a good chance that's what it is.

Locking up a target in STT will get you a 'buddy spike' call if it's a friendly. Again though, be careful with this as radios can be damaged.

Once you have a target locked, you can padlock it. A red box on it indicates an enemy and you can padlock this way outside the normal 10 miles. (not sure if you get the coloured box though). Blue is friendly and green is unknown.

All this said and done, real life pilots can't engage targets at will. They have to be sure that they are shooting at the enemy and even IFF is no guarentee that you don't have a freindly locked up. IFF only sends out a code. If it gets the wrong response then it does not show as friendly. If the IFF is damaged or wrongly coded, they can be mistaken for enemy.

Having flown falcon for the last 3-4 years, I've never needed IFF. You really need more than just reliance on IFF to qualify your target. This is a study sim and you'll find that there are many years ahead of learning how to play this sim. To date, no other sim has come close to offering what F4 has and it's almost 10 years old.