my father calls the "walk" buttons at traffic lights, "politician buttons". I never understood the answer, and thus the joke, as a child... went something like this:
Dad: "why do you always press the politician button?"
Me: "why do you always call it a politician button?"
Dad: "because it does nothing."
Though I'd argue too many analogues of the "politician buttons" still do things -- like give people a "walk" sign while perpendicular vehicular traffic gets a green light.