Coudal's Dear Cell-Phone User SHHH Cards

Why not express your frustration with noisy cell phone users by distributing a nicely designed SHHH card [pdf]? Fun idea from Coudal Partners... yet they do suggest "handing one out and then leaving the immediate area." They also admit in this Wired article that they don't know of anyone who has actually used the cards—perhaps people prefer the adrenaline charge of verbal confrontation over diplomatic typographic messages (which recalls a recent Overheard in New York, where someone's attempts at creative insults were thwarted by a man who calmly said, "This is New York, son. A simple f*ck you will do.").