I fly a lot of aircraft and it's very hard to keep track of wingmates or liberators that need protection. As soon as the first fight starts you basically have no idea where your mates are.
My proposal comes from another game, Tribes. It allowed you to put markers on players / vehicles themselves. This made it a lot easier to track your mates even if they're miles away. Below are some pics that illustrate this feature. I think Planetside would definitely benefit from such a feature as it would make these awesome escort missions less frustrating.
Further additions, maybe unlocks with certs, would for example show even the health of the player / vehicle.