What you saw the referee signal is actually called Illegal Helmet Contact. You can have illegal helmet contact in high school football without an automatic disqualification. Illegal helmet contact covers more areas than just targeting, like spearing, butt blocking, and face tackling.
NFHS Rule 2-20: Helmet Contact - Illegal, Targeting
ART. 1 . . . Illegal helmet contact is an act of initiating contact with the helmet against an opponent. There are several types of illegal helmet contact:
a. Butt Blocking is an act by any player who initiates contact against an opponent who is not a runner with the front of his helmet.
b. Face Tackling is an act by a defensive player who initiates contact against a runner with the front of his helmet.
c. Spearing is an act by any player who initiates contact against an opponent at the shoulders or below with the crown (top portion) of his helmet.
ART. 2 . . . Targeting is an act by any player who takes aim and initiates contact against an opponent above the shoulders with the helmet, forearm, hand, fist, elbow or shoulders.