How about intelligent enemy GV tags?
IE: A whirly in the middle of a forest, hugging a tree, engine off, and holding fire (meaning if he wanted to he could start shooting at planes that are close enough overhead). His tag will be hidden unless your really really close (enough to visualy see the difference between his vehicle and the tree he's hugging and say another tree with a large stump under it). Now lets say he starts firing, now his tag is visible for at least 3000 meters. Logicaly this makes sence, a GV shooting up into the air with tracers on sticks out like a sore thumb from over a mile away.
This would be beneficial in that people could hide in their GV if they wanted to stay on the down-low and play an intelligent sortie. This would also make it so if they weren't trying to stay on the down-low, they would stick out from as far away as they should.
As for tanks (the example I gave was an AA GV) they dont shoot straight up in the air with a MG most of the time, but when they do fire their main gun it creates a large muzzle flash and a large amount of smoke and/or dust imediatley around the tank... so the intelligent tags would work for them in the same way too.
There are some downsides to this I see, one being that lets say your trying to stay on the down-low from circling aircraft, but then a lone tank sees you and starts firing at you. You return fire to the one target that sees you, but now your clearly visible to everyone circling above that didn't know you were there. It's true someone did blow your cover, but until you decide to shoot back he's the only one that clearly sees you (and once you shoot back, everyone within range will be able to see you, weather or not they were actualy out there looking for you or not).
But I think it would work well since in most cases when you're not looking to pick a fight you probably won't win you'll be doing so in a lower profile. And if you go charging in with guns a-blazing looking to stir up some trouble, then you'll do so quite well.