My boys seldom acted up in public when they were little (they've made up for it since). I really dislike when you hear a parent yelling at their kid in public, so, if one of them was being naughty I would just say, "Look at my face" and give them the angriest face I could muster. Most of the time they wouldn't even look at me, but they always stopped misbehaving!
Btw, that face also works on husbands.