These are numeral pennants used for signaling numbers 0 through 3 (though ones for 0 through 9 exist).
A German car pennant for admirals used from 1933 to 1945.
A similar one was used for other members of the Navy:
A car pennant for German Navy Battalion Commanders used from 1933 to 1945. A similar one was used for Brigade commanders:
A Germany car pennant for division commanders used from 1933 to 1945.
A German Navy church pennant.