A while ago here in El Chorro where I live, I began doing 'fist bumps' whenever I was/am near another climber, whether ascending or descending (never when either would fall!-usually when one has just made a clip from a solid stance and the other is descending) and now other climbers have been copying me so I figure maybe others would like to join in this silly but fun action.
if both climbers are close enough, just reach across and bump fists. It gets lots of smiles from the climbers and also the belayers and others at the base of the climbs. It is easy to do here where many climbs are close together.