Actually the French and West German governments had agreed upon a "Europeanization" of Saarland which would have given the area an autonomous status. But the people in 1955 voted against the plans that the chiefs of government, Adenauer (DE) and Mendès-France (FR), had for Saarland.
In 1947 the French franc became the sole legal tender in Saarland. As from July 1954 Saarland issued its own "Franken" coins which had the same specifications (size, weight, etc.) as the French "franc(s)" counterparts. Five years later, in July 1959, the Deutsche Mark replaced the franc/Franken cash in Saarland.
Next year Germany will issue a €10 coin commemorating the 50th anniversary of Saarland's joining the Federal Republic. This picture
http://www.bbr.bund.de/wettbewerbe/grafik/saarland1.jpg (not a great photo ...) shows the winning design. The text says
50 Jahre Bundesland Saarland, and the edge inscription says
Deutschland - Frankreich - Europa.
Christian