The exact style of sconce was used in a very famous "location" in the early part of the twentieth century. It was (and still is) one of the most famous locations in the history of the century. You probably have seen photos of the actual room in which they were installed. Even if you haven't, I'm fairly certain you have seen the sconces in the movie set which reproduced the room in every possible detail.
Big hint: Though they remained in the same room in which they were installed for a long time, no human being saw them for over seventy years.
And since then at least one of them has been sold at auction.
And if your vast knowledge of French antiques fails you, I'm sure you can fall back on your feelings to find the answer...especially if it's a sinking feeling.