This image is in the public domain according to German copyright law because it is part of a statute, ordinance, official decree or judgment (official work) issued by a German authority or court (§ 5 Abs.1 UrhG).
This image of a historical traffic sign is public domain. It was part of the German Road Regulations (StVO) since 1934 or older government regulations. Sources of this signs are the German traffic signs catalog (Verkehrszeichenkatalogs, VzKat) or other statutes, ordinances or official publication like the Reichsgesetzblatt, the Bundesgesetzblatt, the Gesetzblatt der Deutschen Demokratischen Republik or the Verkehrsblatt.