What did every Jew have to wear?

Elie Wiesel's Night is a semiautobiographical story, and, as such, the treatment to which the Jews are subjected in his book are a representation of the way the Nazis treated Jews in Romania, where Wiesel grew up before he was transported to the concentration camps along with his family.
Jews in Romania, as well as in Germany, Poland, and other countries subject to Hitler's demands, were expected to wear a yellow Star of David somewhere on their clothes. This star served to mark them out as different and to ensure that everyone who interacted with them knew the person wearing the star was Jewish. Refusal to wear the star was made against the law. Wearing the star also meant that Jews would be unable to break other rules, such as entering shops where the signage indicated that Jews were not welcome.