This is Warsaw Ghetto Wall historical location marker on the floor of the street.
Many of those signs are located in the places where the wall between Jewish and non-Jewish parts of town was built.
To create the Warsaw Ghetto, the Germans built 11 miles of brick walls around the Jewish quarter.
This area was then closed to outsiders from November 15, 1940 up to 1943 when the Ghetto was liquidated.