[crazy voyager]

Under FIBA it goes like this
Three points in Trails area, as it is for evryone (I think) show the signals, only trail. Lead does nothing (he shouldn't be looking at the ball up there anyway so if he does you know he's looking at the wrong thing, anyway
If shot goes up along base Lead holds "three-point attempt" signal. Trail Mirrors, Lead holds this until he see trail mirroring, he then takes the hand down- even if the shot goes in! (if he's unsure if trail see's he can hold the three fingers up, but lead should never show "made three point attempt".)

But again that's fiba, it only applies to Olympics, world cups and other small stuff ^^