S(chweiz)-Bahn.

The Badischer Bahnhof is located on Swiss territory, but due to the 1852 treaty between the Swiss Confederation and the state of Baden (one of the predecessors of today's Germany), the largest part of it (the platforms and the parts of the passenger tunnel that lead to the German/Swiss checkpoint) is treated as an inner-German station and is operated by the Deutsche Bahn. The shops in the station hall, however, are located in Switzerland, and the Swiss franc is used as the official currency there (although the euro is universally accepted).

Wikipedia: Basel Badischer Bahnhof