The postcard from the French mail artist Zack leaves much space fore interpretations. E.g., the text on the right side says:
20h combattimento. La théorie du cygne noir.
In English: 20:00 fighting. The theory of the black swan.
Other crumbs of text refer to a young conductor and to the story of Tristan and Iseult which dates to the 12th century and was retold in Richard Wagner’s opera Tristan und Isolde.
When I put all parts of the puzzle together, I think… that maybe I should stop interpreting dadaistic pieces of art.