Surfski Knowledge Base

There does not seem to be a universal set of signals agreed on by all, but here is a basic set that many do use and can serve you well:

From tsunami rangers article

A raised vertical paddle or arm usually means to gather around the paddler giving the signal

A raised horizontal paddle or raised fist means stop and hold position. A waving paddle or arm is usually understood to be a distress signal; use this if you need help. Patting the top of your head with one hand means “are you okay?” The same signal is returned if the paddler is okay, otherwise it is assumed there is a problem.

Boat Ed Pictures of the Basic Set of Signals