In the early middle ages, a distinctive feature of Jewish dress was the pointed or a funnel shaped hat worn by Jewish men throughout northern and western Europe. Its use was so widespread that by the twelfth century, the hat had become a Jewish symbol, proudly displayed on Hebrew manuscripts, medieval seals, and coats of arms.
(Image from A History of Jewish Costume)
The Judenhut (German for "Jewish hat"; Latin: pileus cornutus) was a yellow cone-shaped pointed hat that was required for adult male Jews to wear while outside a ghetto in Medieval Europe in order to distinguish them from others. The Fourth Council of the Lateran of 1215 ruled that Jews must bear this stigma. This decision was upheld by the Council of Vienne. Pope Paul IV determined in 1555 that it must be a yellow, peaked hat. A Judenhut could also be used as a stigma for usurers and magicians, not necessarily Jews. As an outcome of the Jewish Emancipation its use was discontinued. Another medieval stigma was the yellow badge, reintroduced later by the Nazis. Parts of this article are translated from de:Judenhut of 13 July 2005