An original WWII German NSDAP detatchment armband here. Narrow variant worn by party members when performing assorted operational duties. An ink stamp is present on the inside of the band, but it is illegible to me. 
 
The NSDAP, officially the National Socialist German Workers' Party, was a far-right political party in Germany active between 1920 and 1945 that created and supported the ideology of Nazism. Its precursor, the German Workers' Party, existed from 1919 to 1920.