Maybe a resident "borrowed" it on a trip to France and put it there for a laugh?
Might even have been put up especially for the occasion. I had a quick look round (to see if there had been a mistake) and there's a 15mph speed limit on the road just south of there, that's a bit strange as well.
The adjacent factory (Unit B4) is operated by Thales and presumably make parts for the TGV, so the French HGV drivers need a reminder of where to go, to take them back to the main road
All well in theory but "Gare" specifically means railway station.
So it's a sign to the High Speed Train Station. In French. In Britain.
I do wonder what would happen if we started sticking double-arrows symbols in France...