The peace sign button was imported into the United States in 1960 by Philip Altbach, a freshman at the University of Chicago, who traveled to England to meet with British peace groups as a delegate from the Student Peace Union (SPU). Altbach purchased a bag of the "chickentrack" buttons while he was in England, and brought them back to Chicago, where he convinced SPU to reprint the button and adopt it as its symbol. Over the next four years, SPU reproduced and sold thousands of the buttons on college campuses. By the late 1960s, the peace sign had become an international symbol adopted by anti-war protestors of the Baby Boomer generation.