A little unobtrusive assistance by some pre-arranged signal can indicate who is speaking.

Outside, by a pre-arranged signal, he links up with a woman waving his mother's scarf.

At this clearly pre-arranged signal her four assistants had risen and left the room.

Alexander, watching their psychological movement, gave his final pre-arranged signal.

As if by some pre-arranged signal, the other two Hawks stepped forward.

Then, on what had to be a pre-arranged signal, all six airplanes flicked their wing lights three times.

Then, as though at some pre-arranged signal, both crabs wriggle free from their homes and exchange shells.

He stopped at the mouth of the cavern as if by some pre-arranged signal.

You may send our pre-arranged signal to the Chief.

You must have a pre-arranged signal and I'd like to see it in action.