This is last flag of the Kingdom of Prussia with regalia removed and black striped changed to red. Out of canvas of SVG file there is similar flag with CoA of East Germany instead of eagle. These two flags I proposed for Prussia after World War II, where Germany was divided in more than two states. Black is changed to red symbolizing Socialism, Brandenburg and Berlin. After fall of Socialism the red is preserved, because black is associated with monarchy and new Prussia is either republic or state of the United States of Europe (see the link for flags of more USE states).