Czechoslovak police arrested two Charter 77 human rights activists when they unveiled a banner during an official May Day rally, Czechoslovak emigre sources in Vienna said. The sources said the two, Tomas Hradilek and Rudolf Bereza, raised the banner in the town of Olomouc. It read, "Charter 77 Calls on the People to Show Civil Courage." A third charter activist, Michal Mrtvy, was arrested for filming the event. The Charter 77 movement has urged Czechoslovaks to move for change through the present political system.