French/German Border Crossings Near Waldmohr
Saarland today is the German state directly west of the KMC, extending from Waldmohr to Saarbrucken. This coal-rich area was taken from Germany in the Treaty of Versaille at the end of WWI and placed under control of the League of Nations until 1935. The intent was to provide a buffer zone between France and Germany and prevent militarization of the border area. Nevertheless, Hitler boldly marched into Saarbrucken on 1 March 1935 and reclaimed the Saarland for Germany. It remained part of Germany until the end of WWII at which time it fell under French administration until rejoining Germany in January 1957.

Vestiges of two border crossings remain near Vogelbach and Waldmohr. These quiet spots give no hint to their importance prior to 1935 and in the immediate post-war period.

The crossing west of Vogelbach looking into what was France before 1935 and after 1945. The cluster of buildings still bears a roadsign reading "At the Old Customs". Several walls of WWII-era concrete remain. The border line was slightly west of the building (see map).
The old border crossing building at Waldmohr is now a restaurant. According to the map, the border crossed just west of the present traffic circle in the trees, and angled northwest along the ridge. A "Welcome to Saarland" sign marks the border along the highway.  My landlady described crossing this border to buy meat and cloth on the black market just after the war. 
Close up maps to the Vogelbach & Waldmohr border crossings