We give credit to another website, stampboards dot com, for describing this unusual and creative item, which looks like a novelty postcard but is actually a SFr 5 mini souvenir sheet that can be played on a record player.  In maximum card style (but without the additional stamp), it seems to have a postmark but we should let you do your own research on this.  Phonograph record stamps have been around awhile, and that they look like postcards means they could probably be used as such.  Unused.  Grade: 1