The French Foreign Legion Cross of Honour appears on the original Grandville illustration from the book "Un Autre Monde" (Another World). The scene depicts a scientist travelling through alternate realities and at this point seeing the juggler of worlds. The satire is not lost on modern audiences, the gist of it is that the all dimensions are merely the play things for forces greater than us. The scientist sees a fireball streak by that looks like the Cross of Honour, which is likely a jab at French foreign policy of the era, that no matter where you go, there they are.
Queen changed it to a banana probably to avoid any political misunderstandings. And bananas have a long history with comedy. And it does eventually tie in nicely with the bananas in the "Slightly Mad" video, though they may not have intended that originally.