[FONT="]It is indeed a penalty.
Rule 7, Article 5:[/FONT]
[FONT="]"Player(s) aligned in a stationary position within one yard of the line of scrimmage may not make quick, abrupt or exaggerated actions that are not part of normal defensive player movement.[/FONT]
[FONT="]"No player shall use words or signals that disconcert opponents when they are preparing to put the ball in play. No player may call defensive signals that simulate the sound or cadence of (or otherwise interfere with) offensive starting signals."[/FONT]