You would not need a special whatnot white-flag system if the game had 3D voip. With positional audio you could just try to surrender by yelling "don't shoot" and ur fate would be on the hands of the enemy. Like many said it is possible, and ppl do it often, in RnL.
I as well kill anyone trying to surrender (they usually are holding a nade in the hand, tricky bastards) or if I see a POW near our cap zones cos holding POWs in our cap zone spawn blocks our whole team. + it takes too much effort to guard a POW, unless the map is made POWs in mind, like rnl_stannum (props for Snuffel!) that had locked cells which were out side of cap zones.
Ps. try circumventing 3D voip surrendering with a 3rd party voip program. Yes, exactly.