You'll find some variance from club to club (and follow your club's rules if they have them), but what follows is a basic list of hand signals used for communication when riding as a group. Always use your bike's turn signals to indicate a turn.
Double File
Index and little finger pointing up. Stagger riders - normally at two second intervals between riders in the same track. May also be index and middle finger as in the V for victory sign.
Gas Stop
Left finger pointing at gas tank. Time for a gas stop (or any other necessity while you're at it). May be used to inform other's in your group you're running low on fuel.
Road Hazard
Single finger pointing down. Watch for road hazard - pot hole, dead animal, etc.
Single File
Single finger pointing up. Spread out and form a single column of riders. Used frequently when additional maneuvering may be required - (twisty roads, bad surface conditions, etc).
Slow Down
Hand parallel to ground and moved up and down. May also be used to warn an oncoming rider of a hazard (speed trap, bad road, etc.)
Stop
Open hand pointed down. Sometimes used to indicate the column should slow down, but easily confused with the driver's manual "stop" signal. Best used as stop at all times.
