This weekend, Parisians found that the ads plastered at their bus stops looked different from usual. That’s because hundreds of them had been surreptitiously replaced by fake advertisements criticising the “corporate takeover” of the COP21 global climate talks currently being held near the French capital.

Brandalism, a UK-based guerilla street art group, inserted unauthorised works by over 80 international artists in more than 600 ad spaces, according to its press statement. Some of the pieces criticised corporations that are official sponsors of the climate talks as well as being big polluters, such as the airline Air France and the energy giant GDF-Suez.

Others took aim at some of the leaders taking part in the talks, including French President François Hollande, US President Barack Obama and Japanese Prime Minister Shinzo Abe.

"State of emergency".

Even if the adverts are taken down, Brandalism’s campaign photos have already been widely circulated on social networks. Many commenters have hailed this as a clever way to protest in a country where it is currently illegal to hold demonstrations, due to the state of emergency enacted following the November 13 terrorist attacks in Paris.