Oooh. You've caught me off-guard here... my rulebook's at home and I'm not.
My instinct would be to signal an illegal attack hit. If the team that is on my left committed the fault, then you blow the whistle, point with the right arm to the team on the right, and then raise your left arm straight up - and then bend it down at the elbow towards the right-hand court.
So your left arm would start something like this:
and finish something like this: