This is a name stone from the Rue de l'Arsenal or Zeughausgasse in Cologne. The dominance of French as the language of administration and the language of the public sphere in the Rhineland after 1801 is evidenced, among other things, by street names.
Rue de l'Arsenal / Zeughausgasse in Cologne, colour photograph, 2010, photographer: Willy Horsch; image source: Wikimedia Commons, http://commons.wikimedia.org/wiki/File:Rue_de_l%27_Arsenal-_Zeughausgas.JPG?uselang=de. Creative Commons Attribution ShareAlike 3.0 Germany.