I saw this in NYC and thought it was a nice way to send a message with the right medium. Rather than advertising on a taxi cab, why not be part of the solution with your marketing. If only everyone thought this way, we'd be in a lot better shape.
I must admit though, I likely miss things that I could be doing better and then there is always conflicting advice. The best resource on this topic that I have seen is the book written by the Union of Concerned Scientists.