Philip Rivers was called for it against the Broncos last season. The league said they'd enforce it more frequently. They said they would give more focus to false starts by the quarterback.
Item 5: Shotgun Formation. A player who is in position to receive the snap in shotgun formation is permitted to shift his feet prior to the snap, but any quick and abrupt movement is a False Start. This includes thrusting his hands forward when there is not a simultaneous snap.
A.R. 7.16 Quarterback A1 bobs his head in an exaggerated manner prior to the snap and draws the defense into the neutral zone. Ruling: Penalize five yards for false start.
Eagle eyed readers of Peter King pointed out that Peyton sure likes to do that quite frequently. They were actually reemphasized as "The Manning Rules", even though they were already in the book. The rule was raised prior to 2012 as quarterbacks around the league were getting away with what was clear false starts, under the premise that it was a pre-snap adjustment by the quarterback.
No, Manning isn't the only one who does it, although his Omaha calls were on display this past weekend. I wouldn't expect this rule to become a point of focus this post-season, although I wouldn't be surprised to see it called early on in the game just to set precedence.
And as Pats fans can understand, rules are rules and they're there to be called, for better or for worse. Even if you've never seen it called before.