[rufibarbatus]

Buses are pretty much ads on wheels, --- and in some buses of the green variety [1] there are TV sets broadcasting most relevant content such as government propaganda, the horoscope, news and events, and yes, advertisement.

[1] I'm yet to figure out what the colours mean on buses.

[alextp]

Regarding [1], each bus company has a different color. The companies won different government contracts for different parts of the city, so the east side is roughly red, the south blue, the north-west green, etc.

[kawera]

Buses in SP have no exterior ads. There are ads inside most of then. The law regulates exterior ads only.