Effective 1 April 1920, German State agencies were required to frank official mail with official stamps (dienstmarken). German Federal agencies had to do the same beginning 1 July 1920.
Early official stamps of the Weimar period were primarily numeral designs featuring the denominations in large-format numbers. Later officials include overprints of German States officials. Finally, later years of the Weimar period saw the introduction of the “Straw Hat” issues, which remained in use from 1927-1936.