I know I'm not the only one who'd be extremely disturbed after seeing the above ad that was actually used in Germany. In fact, I wouldn't be surprised if it made a few children cry, even if the pigeons were only plastic. Regardless, it is certainly an effective ad, even in today's media-saturated world, and it's included in the Web Urbanist's list of Creative Billboard Advertising Campaigns.
As cool as these billboards are, they aren't always consequence free. I remember when I was a kid and San Diego got its first clever billboard like this. It was a 3D cheeseburger that emitted real steam. So many people thought the billboard was on fire that they eventually had to shut it off.
See Also: 9 Innovative Outdoor Ads