Someone left this in a prominent place on a high street.  I - and I am sure, they - hope that everyone who walked past saw it and took it on board.  It's a small town - say 200 people noticed that sign in a day, and began to live by its message.  They then pass on the message to 10 friends each, who pass it on to 10 more...theoretically, pretty much the entire World becomes a more forgiving and tolerant place.  Well, even if this doesn't happen, at least whoever left the notice there can feel happy that they at least tried to start something.