One special thing about bus advertisements surely is the oppurtunity to do commercial for brands as well as for public political campaigns.
This way of advertising is relatively old , starting in the early 20th centuries on streetcars. For a couple of years now, it does not only appear on the outsides of buses but in the inside as well: in several countries displays were installed that can show short films or simply animated posters. In a couple of countries it is even allowed to print the tickets with some commercial messages on them.
Besides the possibility of using public transport busses to do some advertising, there is also the alternative to hire a bus and use it as in a special private way. This type usually is used for political campaigns or specific promotions for one product. For this purpose, open-top busses are mostly hired, so that an interaction between the people on and off the bus can take place.