In the post-World War II period of the Cold War, New York City’s May Day parades attracted the trade unions and other organizations that were associated with the left.  Banners, like this one at the head of the 1948 parade, called for peace.  Participating organizations encouraged their members who were World War II veterans to wear their service uniforms in order to counter the charge that they were “unpatriotic.”

Image from NYC Central Labor Council Collection, Robert F. Wagner Labor Archives, New York University