Concentration Camp Money.

During World War II, Germany created special currency (more like scrip, really) specifically for concentration camps. These were often created by the Jewish prisoners and many were quite intricate. Concentration Camp Money are collectible because of their historical reasons and as a reminder of the Holocaust.

From the website:

The concentration camp money(scrip) shown above was used by inmates and had no convertibility outside the camp. This had the effect of denying escapees from having any money to spend if they escaped.

The Concentration Camp Money above was issued in the Westerbork [wiki] Concentration Camp (where Anne Frank [wiki] and her family were taken.)

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