The MPAA Thinks You're Stupid | The A.V. Club:
Still, the Motion Picture Association Of America doesn't want to take any chances, which is why they told the director of Watchmen, Zack Snyder, that he couldn't have a guy pointing a gun at the audience in the trailer. Snyder replaced the gun with a walkie-talkie. This way, if anyone from 1903 watches the trailer, instead of ducking and/or running for their life, they'll just drop their bowler hat, curl up into a ball, rock back and forth, and mumble into their shirtwaist, "What world is this? What is happening to me? Where am I?"
From MTV Movies Blog:
“[The assassin] has a gun,” Snyder explained. “So the MPAA said, ‘Look you can’t have him [holding the gun]‘ … I don’t even think it’s one second. I think it’s like 12 frames. He’s pointing the gun at the camera, and they said, ‘You can’t do that.’”
For years, the MPAA has prohibited weapons from being pointed at the “viewer” in advertising, presumably for fear that it will freak them out. That’s why you always see guns pointed at angles on movie posters and in film trailers.
Good job, MPAA. It's good to know that someone is looking out for people from 1903 who have maybe fallen through wormholes, and/or people in America who have never seen a movie or television before. You know what else might freak out and produce visceral reactions in those people? Movies in general. They can be very upsetting. Someone should really do something about all the movies these days.