From Der Spiegel (in German), there is notice of a market which surprises even me. Many Parisians ("Schwarzfahrer") don't pay to ride and Metro and risk legal fines. For seven Euros a month, you can buy insurance against having to pay those fines. The group also considers itself part of a protest movement for the right of free public transport.
Talk about adverse selection… Presumably it's understood that you don't pay the fare and the relevant risk is simply how often you are caught.
For the pointer I thank Steffen Reinhold. Ferdinando Monte sends along this English-language version.