How effective are posters in altering people's perceptions? Are they only worth the paper they're printed on or are they truly persuasive papers? The debate rages at the exhibition Signs of Change: Social Movement Cultures 1960s to Now at Exit Art in New York, where hundreds of posters, photographs, moving images, audio clips, and ephemera document more than 40 years of activism, political protest, and campaigns for social justice. Many of them have indeed altered perception and triggered action. Curated by Dara Greenwald and Josh MacPhee and organized thematically, the current show presents issues from Civil Rights and Black Power in the United States to democracy in China to anti-apartheid in Africa to environmental activism and women's rights internationally. "The exhibition also explores the development of powerful counter-cultures that evolve beyond traditional politics and create distinct aesthetics, lifestyles, and social organization," say its organizers. Exit Art exhibitions are famous for presenting a critical mass of unique artifacts and this one is no exception.