The stamp shows us a scene from the opera “The Flying Dutchman”.
The vessel depicts is a topsail schooner, viewtopic.php?f=2&t=12482 if it is the THETIS I am not sure. Also, a portrait of Richard Wagner is shown.
Wagner, Richard: ... (1813-1883) When Richard Wagner left Riga as the conductor in 1839 on the topsail schooner "THETIS" to escape his debtors in Riga. She sailed to England, Wagner read on board Heine's fragment "From the Memoirs of Herr von Schnabelewobski" with the story of the 'Flying Dutchman' in it. He listened to the opening bars of the famous sailor's song in Wagner's opera for the Pillau sailors' call to work as the sails were set.
More is given on: viewtopic.php?f=2&t=9920&p=18544&hilit=flying+dutchman#p18544
https://en.wikipedia.org/wiki/The_Flyin ... an_(opera) Navicula.
DDR 1963 25pf. Sg E678, scott?
Germany 1933 4p + 4p sg 514, scott?