Old fashioned school duplicating machines required the operating handle to be left in a straight down position to prevent ink leaking out whilst not in use. many of these had signs stuck on asking users to ensure that this happened.
One in particular I saw said ''please leave the handle at six o'clock '' to which some one had added ''sod that I go home at five''
The best sign i ever saw was on a durex machine in the pub gents. 'Made to British standards', it proclaimed. To which some wit had scratched underneath, 'So was the Titanic'.
The PE staff changing room, at the school that I taught at, had a filing cabinet drawer labelled "PE Stationary". I often wondered how that was accomplished ;-)
My boss decided to put up signs around the building to encourage various aspects of safety. In the staff washrooms he had a large sign with " Think" written on it above the hand basins. This stayed up until somebody put up a sign beside the soap dish, which read "Thoap".