How exactly do the tracer pistols work?

I don't think I totally understand what the effects of the tracer pistol on a vehicle.

Does it provide auto-guidance to other weapons? Which ones?

Does it just display the location of the vehicle?

Solution 1:

• Darts can be fired either from the dart pistol or as secondary action by the Apache/Havoc gunner if he has alternative weapons package;
• Dart gun is the only weapon in BC2, which doesn't have any bullet drop at all. So don't aim above the target. Also even though it's almost silent, it will disclose your position as dart leaves red smoke trail;
• Once your target is marked with the dart, there will be voice notification for the whole team, also if you're close enough, you can see actually see it as little red light flashing;
• All of players on your team can take advantage of any dart placed by any team member;
• You get points if vehicle darted by you is damaged or destroyed by someone else;
• Darts work with RPG-7, Carl Gustav and Apache's Hellfire;
• Darts do NOT work with laser guided missiles: M136, stationary AT, UAV's Hellfire;
• You have to keep the dart indicator in the launcher sights to get lock-on. Direct line of sight is not required, you can get lock-on through wall, terrain etc. The indicator will turn solid and distance to target will be displayed when missile is locked-on;
• Missile guided by dart will fly straight in whatever direction you fire it for a second, then it'll fly straight towards dart. It will not avoid any obstacles in between. Thus the best tactic is to fire up towards the sky;
• When you're in vehicle hit by dart there will be beeping alarm and red flashing text "missile lock", can't miss it;
• Smoke-screen upgrade to vehicles removes any darts on them when used;

Solution 2:

Here is how you have to do:

• Fire the dart at a vehicle (or a soldier, it's funny ;)
• Select one of the weapons using the darts guidance (RPG-7 AT, M2 Carl Gustav AT but not the M136, which is not compatible with darts)
• Find your taget and aim (you will see a yellow rectangle), then hit the magic multi-purpose select (on PS3, should be Q on PC). You will then see the live distance of the target, meaning it's acquired.
• You can now fire. It is better to aim high (sky for example) or a free area, so the missile will be able to maneuver to the target.
• BOOOM
• Enjoy your well earned points

You can of course be the one who fires the darts and the missile but it's not mandatory. You can sometimes see the flashing beacon on a vehicle and just aim, acquire and shoot.

Solution 3:

According to the Battlefield: Bad Company wiki the darts it fires can be locked on to by the RPG-7 and M2 Carl Gustav launchers, but not the AT-4.