This signal is used by the Referee to signal that a personal foul has been commited. It is often followed by another foul signal when it indicates the severity of the second foul (e.g. a 15-yard facemask foul rather than a 5-yard one).
PenaltyWhen against the defense, this always results in an automatic first down. It attracts a 15 yard penalty, but the assessment spot depends on the type of foul although most are from the basic spot.
One arm is held in front of and across the body just above head height, and the second is held slightly higher and brought downwards in an unhurried motion simulating the striking of the first arm (you should not actually hit the first arm - it hurts!).
Finally point to the offending team by stretching an arm out from the shoulder to the horizontal.