Palm down to rear, slow down. Hand or fist up, stop. That, plus turns and pointing out road hazards, seem to be consistent from group-to-group (in my experience).


However, even a simple "hazard on the road shoulder" has lots of variations (some point at the hazard before the familiar hand-behind-the-back motion, others do some kind of wave or wiggly hand, etc)... so instead of assuming some standard, best to get accustomed to what the group uses and stick to it on a per-group-basis to avoid causeing any sort of internal group confusion.