Oooh, I thought of another one!
Here in MD, they use the slogan "Click It or Ticket" to remind people to buckle up. (Not sure if it's used in other places as well.) One day, my cousin's husband was sitting in traffic and saw that slogan on a lighted sign. Unfortunately (or, rather, fortunately), some of the lights were out. So the sign read:
LICK IT OR TICKET!
That picture almost got me in trouble at work because I burst out laughing when I saw it.