How about a [link=http://www.nightbeacon.com/lighthouseinformation/articles/Lightship_Day_Markers_Hull_Colors.htm]Square Day Marker[/link] mounted on top of the tank or attached to the aerial? I would be 3 dimensional so you'd be able to hit it from all sides.

I still prefer paintballs through wireless cameras. Where else do you get the feeling of actually being in battle? Certainly not from standing over it. 2 hits to the front for a kill, 1 for the sides or rear. If it's not a good shot, the paintball either won't burst or will bounce off, skill counts! That's not all, you must capture the other side's flag with your barrel and get it across the middle of the battlefield to win. 3 tanks on each side, 4 or more if using alternative electronics as we're limited to 7 frequencies with HL.