[Reffing Rev.]

Our crew uses a ton of signals to communicate between us...mostly because I turn deaf when I put on stripes.

Arms crossed in X in front of body - more than 10 yards for 1st Down
Fists pounded on top of each other - Clock stops after this play. (4th down)
Arms crossed below the waist (optional snapping of fingers) - clock starts on the snap.
Rolling finger - wind the clock on the ready.
One hand on the hip - Offense is waiting for the play-clock (usually R putting his hand on the belt where BJ has his "ready-ref")
Waving a hand underneath 1 finger - Less than 1 minute left on the clock. (usually between BJ and R, when echoed we both point at the official who has the clock)
Waving a hand underneath a snapping finger - Play clock is off
L shaped fingers - L(ong) goal line, wings stay ahead to goal line.
BJ or R pointing at pylons - wing move to pylon on snap.
BJ or R with hand on chest - "My goal line"
"T" shape with hands - Kicking tee coming on the field, assume field goal positioning.
Tapping the Nose - "I smell something" - trick play coming

There might be some others that are situational and I can't think of them sitting at my computer now. Maybe I should go put on a striped shirt.