Redwood City, CA has actual, printed signs scattered around that say things like:

“Traffic school is boring. Slow down.” “Speed limit 25 mph. It really won’t hurt.” “Is today the day your speed hurts a child?” “In a hurry? A speeding ticket will make you late!” “What don’t you understand about 25 mph?”

and maybe a dozen more. They’re actually great indicators that the city doesn’t enforce the speed limits. Which makes the “ZERO TOLERANCE” speed sign the funniest one.

Edit: The city of Hayward, CA has a pedestrian crossing sign that says something to the effect of “Heads up! Cross the street, THEN update Facebook.”