Switzerland has a system of citizen initiated referenda. From the level of the Commune (the local level of government) to the Canton (the building block of the Swiss federation) there is a system of propositions being put to the people for decision. Each referendum (sometimes several are held at the same time) generates official sized posters for and against propositions.
This image taken in February 2008 depicts a referendum poster on the back of public bus. The proposition for this referendum was to make public transport free in the Canton of Geneva. This poster argues against making public transport free. The referendum was held at the end of February 2008. The move to make public transport free was rejected by the people of Geneva.
There are sound arguments for making public transport free to discourage the use of motor vehicles. It is interesting that this Swiss Canton rejected all these arguments.