Yellow badges (or yellow patches), also referred to as Jewish badges (German: Judenstern, lit. ‘Jew’s star’), are badges that Jews were ordered to wear at various times during the Middle Ages by some caliphates, at various times during the Medieval and early modern period by some European powers, and from 1939–1945 by the Axis powers. The badges served to mark the wearer as a religious or ethnic outsider, and often served as a badge of shame…
After the German invasion of Poland in 1939 there were initially different local decrees requiring Jews to wear a distinctive sign under the General Government. The sign was a white armband with a blue Star of David on it; in the Warthegau a yellow badge in the form of a Star of David on the left side of the breast and on the back. The requirement to wear the Star of David with the word Jude (German for Jew) – inscribed in letters meant to resemble Hebrew writing – was then extended to all Jews over the age of six in the Reich and the Protectorate of Bohemia and Moravia (by a decree issued on September 1, 1941, signed by Reinhard Heydrich) and was gradually introduced in other German-occupied areas, where local words were used (e.g., Juif in French, Jood in Dutch).
One observer reported that the star increased German non-Nazi sympathy for Jews as the impoverished citizens who wore them were, contrary to Nazi propaganda, obviously not the cause of German failure in the east. In the Protectorate of Bohemia and Moravia, government had to ban hat tipping toward Jews and other courtesies that became popular as protests against the German occupation. A whispering campaign that claimed that the action was in response to the United States government requiring German Americans to wear swastikas was unsuccessful. (Source)