This article discusses fly-posting practices performed by radical urban activists in Rome and Berlin. It suggests that political posters cannot be understood simply as channels of information about events and activities of political and subcultural "autonomous scenes" encompassing squats, occupied social centers, political bars, bookshops, cafes, and similar activist hangouts. Rather, these "street media" are crucially involved in processes of spatial appropriation and in the construction of an antagonistic territoriality. Fly-posting exposes its practitioners to police repression and attacks by right-wing groups, and given the risks involved, it also becomes a form of demarcation, alerting that a certain wall, street, area is symbolically claimed by the movement. Looking at fly-posting we can come to understand the nature of autonomous movement scenes as antagonistic and exclusive spaces, whose internal communitarianism is premised on the symbolic and spatial repulsion of authorities and political enemies.