CERN (and the LHC ring) crosses the borders of Switzerland and France in several places. This is one of them.
There is a perhaps fanciful story passed along by a CERN oldtimer that the border of Switzerland and France was slightly modified in a small section of CERN to avoid French regulation of one of CERN's two restaurants. When we sighted along what this marker indicates is the border (see those little lines on top of the marker?), sure enough, the restaurant was barely on the Swiss side.
