As I read the thread about the Chili's = Chili's conspiracy, I suddenly remembered a funny bit of vandalism that occurs frequently on the trains in the city I live in.
If you live in Sydney, you've most likely seen this before. It's kind of like the entire city's in-joke.
* originally: At night, travel near the guards compartment marked with a blue light
When have you seen funny vandalism and what did it say/suggest?