From th site http://spdnet.sozi.info/bayern/muenchenland/pullach
a flag of the Ortsgruppe Isartal of the Reichsbanner Schwatz-Rot-Gold (Reichs Flagg Black-Red-Gold). The Reichsbanner was a Paramilitary Organisation of the German Socialdemocratic Party - SPD. Its role was to protect SPD-meetings from attacs of the Nazi SA. After the Nazi came to power in 1933 the Reichsbanner was banned and its members prosecuted. The symbols of the Reichsbanner was destroyed, and so not many Colours was preserved one of these was those of the Ortsgruppe Isartal.