Warsaw Ghetto postal card, denomination 50, never issued

http://lod.ehri-project-test.eu/units/us-005578-irn537029-irn548100 an entity of type: RecordSet

The Warsaw ghetto stamp was donated to the United States Holocaust Memorial Museum in 2016 by the Katz Family. 
1941 April 
irn548100 
Warsaw Ghetto postal card, denomination 50, never issued 
overall: Height: 4.250 inches (10.795 cm) | Width: 6.000 inches (15.24 cm) 
Warsaw ghetto stamp marked 50 issued by the Warsaw Ghetto Resistance Organization (Żydowski Zwia̜zek Wojskowy). The Warsaw Ghetto in Poland existed from October 12, 1940, to May 16, 1943, when the Ghetto was liquidated by German forces. The stamps were manufactured in an effort to establish a ghetto mail office by the underground, but were not issued for use. This stamp is one of more than 900 items in the Katz Ehrenthal Collection of antisemitic visual materials. 
No restrictions on access 
No restrictions on use 
Paper rectangle for postal use with a graphic design stamped in blue ink on the front with the denomination 50, 18 Stars of David of different sizes, a fence, a flame with the SS runes, and acronyms. The reverse is blank. 

data from the linked data cloud