Rather than yelling up “off rappel”, which may or may not be heard if it’s a windy day or you’re out of sight, try this instead:

when the rappeler is safe on the ground or at the next anchor and off rappel, she grabs a strand of the rope with each hand, and pulls the strands back and forth in large arm motions, several times.

This does two things.

1. It silently signals the remaining climbers that they can begin their rap set up.

2. It ensures that the ropes can pull freely. If the ropes are crossed, or hung up or in someway making the rope pull difficult, this can hopefully be remedied by the next climber down.

This tip is originally from Topher Donahue via Climbing magazine