In the US army most forward observers (fisters) go by fox call signs. "Splash over" is used typically by artillery gunners over comms during fire mission to denote munitions fired. "Splash out" is used by the observer over comms to confirm observation of impact.
*Trained
If it's AF. On ground it would be call sign. Since Q was talking about operators in harm's way I'm thinking either SF or rangers on ground.
I bet that was a slow process
Reading over qmap is like listening to military comms.