Checkpoint Charlie

From 1961 until 1990, Checkpoint Charlie served as the main crossing point for Western personnel leaving West Berlin to enter the Soviet East. Necessitated by the building of the Berlin Wall in an effort to stop an exodus of defectors, the checkpoint became a symbol of a divided Berlin. The Allied side consisted of little more than a temporary hut and a now-iconic sign that read, in four languages, "You are leaving the American sector." What chilling 1962 incident sparked protests there?