"Canzone del maggio" is the song by Fabrizio De André this strophe is taken from, and it's part of an album called "Storia di un impiegato", published on 1973.

The whole album has a very strong political connotation: this particular song is inspired by the songs the protesters where singing during the french 1968 riots (the original inspiring song is "Chacun de vous est concerné" di Dominique Grange).

According to this scenario, the poster design reflects the cyclostyled posters the protesters were used to hang poster on the city walls to spread their ideas.