L'Atalante (movie)

I recently came across a reproduction of the poster of an old French film, directed by Jean Vigo in 1934 and called "L'Atalante". You can see a tiny scan of a video cover here , that includes this poster.

The film is set on a ship, called L'Atalante, that apparently flies a swallow-tailed flag with a light disc shifted to the hoist, charged with a dark (perhaps black) uppercase "R". Apparently because I didn't see the movie itself, but this flag appears on the poster, both as a flying flag and as a drawing on the ship's stern (see attached details).

Now, this flag looks familiar but, apart from a micronation called Empire of Runion, that chose something very similar (red swallowtail with a white disc and a black *crowned* R), I can't pinpoint it. Is it real? Is it fictitious? Did anyone here see the movie and can tell if the flag indeed flies in it?
Jorge Candeias, 27 July 2003