Repère de Nivellement, Rue de Sévigné

I was intrigued by this tiny plaque on the side of what is now the musée Carnavale Histoire de Paris (http://www.carnavalet.paris.fr, closed for renovation until 2019). EDIT: [Jose Gabriel Gomez](https://sketchfab.com/aerographstudio) has informed me that this is a topgraphic plate indicating the plaques altitude above sea level. EDIT 2: [Calin Suteu](https://sketchfab.com/calinsuteu) has kindly shared [this article](eauterrefeuair.wordpress.com/2016/03/08/reperes-du-niveau-deau-a-paris/) which explains a bit more about the plaques and also has some great images of similar examples in much better condition. Approx. 25cm x 20cm See if you can spot it on this streetview image: https://goo.gl/maps/9YTb6sK4LFB2