This method of persuasion is effective because it shows people getting hurt or about to be hurt because of you doing something wrong as it is something you can prevent. It hits you like a stab in the back, for example the poster that the man was dying to save a life which could be yours brings you into a wholenother perspective. This method of propaganda will encourage people to do whats right. This could be for them to join the army or something as little as giving a friend a ride.
Not the best answer but i got it correct hope it helps;)