This signal is used by the Referee to indicate illegal contact by the helmet. This is considered a dangerous foul for both the perpetrator and the recipient and so is a personal foul.
Penalty15 yards from the basic spot and an automatic first down if against the defence.
Firstly execute the Personal Foul signal (S38), then raise one hand to tap the side of the head in an unhurried manner.
Finally point to the offending team by stretching an arm out from the shoulder to the horizontal.