Don't even joke about killing an innocent Goldfish!
or flushing your exs sweater, it should be used to wipe the crap of your chain before posting it back to them with a thank you note.
more seriousness in the form of intelligent road signs now.
about 14 yrs ago while touring the lake district on my motorcycle i came across sign next to a power sub station saying this area is prone to flooding, if this sign is submerged do not park here.
also a caravan park we stayed at last year had a sign beside the entrance/exit asking people to stay of the road & if exiting the caravan site on foot to use the pedestrian exit & not the car exit (seems like a fair statement) until you notice the only pedestrian gate was on the other side of the road that were forbidden to walk on.
Also same place had a sign on the water taps saying running water is turned off from 10pm, if water is needed after this time use the water supply in camp sites kitchen beside shop. The campsite kitchen had a sign saying kept locked at nite time open from 7am-9pm.