Yes, it's a good idea to slow down and drive safely in these neighborhoods. No it's not a good idea to put up fake signs on this scale, you're not much better than graffiti artists. 

Because of the tactics involved people who would otherwise be supportive are talking about tearing these signs down. It's one thing to have a good idea and shop it around to the city and neighbors it's quite another to become a self-appointed arbiter. 

"Agent 1" is simply a coddled child unable to come to terms with how grown-ups approach issues in an adult world. This idiot simply chose to alienate everyone rather than take the time to develop a long-lasting solution.