Making signals for the crowd

[DC_Ref12]

Something during the Duke-GaTech game on Sunday that got my attention: Virginia Tech player was wide open (kind of cherry picking) under his own basket, received a pass from his teammate and bobbled the ball while shuffling his feet, got control of the ball and went up for a layup. Crowd went crazy wanting a travel, and the L correctly did not call it. Then before he started back up the court L makes a bobbling motion with his hands, and this seems to quiet the crowd down.

The L was nowhere near either of the team benches, and completely at the opposite end of the floor from the Duke bench, so I'm not sure he was making the signal for their benefit. It seemed like he was making the signal for the crowd.

So, in what instances is it acceptable to make a signal like that which is not prescribed (I'm also thinking of the wiping hands motion that is made for a blocked shot) and in what instances is it acceptable to make those kinds of motions in order to communicate to the crowd?

Thanks.