U.K. agency Brothers and Sisters teamed with German street artists Mentalgassi on "Making the Invisible Visible," an outdoor campaign for Amnesty International to bring attention to the case of Troy Davis, a prisoner who has been on death row for nearly 20 years for murder, despite serious doubts about his guilt. The special posters are designed so that head on, they appear to be mere bars. But from an angle, Davis' face becomes visible. An accompanying plaque also directs observers to a site where they can petition to stop Davis' execution.