It is a
Protos Type C1, built by the "Protos Automobile GmbH" (part of the Siemens Schuckert Werke/Berlin). Maybe you´ve found it with the
Protos 10/45 PS tag. That claims it 45 horsepowers and 10 "SteuerPS" (tax-related HP) or as the NAG Protos 14/70 HP (Siemens merged with NAG in the 1920s)
The Protos Type C1 in its different variations as 10/45 and 14/70 was built from 1924-27
The license plate shows that this one survived in the former GDR (East Germany) behind the iron curtain. It is a plate that was just used on very rare and special vintage cars. A "5" in the first place was used for pre 1930 cars with more than 20HP:
http://www.nolinks.htm