I saw one of these posters at 6th and Josephine the other day. They're put up by a group called denverkillsdogs.com, which opposes Denver's ban on pit bulls. I found the ad pretty confusing when I first saw it. (Actually, the one I saw showed a picture of a woman hugging a dog, and I wasn't sure if the ad was insulting the woman or suggesting that she was going to be killed by the city or something.)
Then there's the ill-considered tag line, "Repeal your breed ban!" It's the "your" that really sucks, making it quite transparent that there are some people outside of Denver who disapprove of its laws. Anyone who understands the ad and might be vaguely sympathetic to its message will probably be put off by the outsiders telling us how to live. "Repeal the breed ban" might have been more effective and less off-putting.
Finally, I recognize that I'm not a dog owner and thus am not likely to be persuaded by this ad in the first place. But I also recognize that there are some concerns out there -- overhyped, perhaps, thought probably not completely fabricated -- that pit bulls are dangerous. The photo above of a pit bull with a cute little kid doesn't make me feel sympathetic to the dog; it makes me worry about the kid.