This signal is used by the Referee to indicate that an illegal pass has occurred. This may be against the offense as follows:
A forward pass from in front of or once the ball has crossed the line of scrimmage
A second forward pass during the same down
A forward handoff to a team mate who is not elligible to receive such a handoff
An intentional backward pass out of bounds to conserve time
This may also be against any player who makes a forward pass following a change of possession.
PenaltyFor types 1-3 above, it will be assessed from the spot of the foul and will attract both a 5 yard penalty and a Loss of Down (S9).
For type 4 it will be a 5 yard penalty from the spot of the foul.
Begin with both hands held by your side and with an unhurried but exaggerated motion move one around to the side and continue until it has reached the small of your back. I believe that this should be exaggerated otherwise it could be missed by the press box.
This will usually be followed by the Loss of Down signal (S9).
Finally point to the offending team by streching an arm out from the shoulder to the horizontal.