In 1967-68 I worked in the chemical lab at Stelco (The Hamilton Steel Company) in Hamilton, Ontario. The washrooms had the graffiti very well organized. One cubical was for philosophers, one for comedians, one for artists, one for pornographers...
One shift we came in to work and discovered that the cubicals had all been cleaned of their graffiti. At the end of the shift, in small, neat block capital letters on the door of one of the cubicals was printed, "F@#& off Cleaning Ladies!"