The Library on this website has a new article, by Mikkel Planthinn, about the Danish Shoulder Flash, worn on the RAF uniform to indicate that the wearer was from the Allied country of Denmark.
Denmark was invaded by German troops on 9 April 1940 and would remain occupied until liberation on 4 May 1945, only four days before the end of the war. Danes in exile fought for the Allied cause throughout the Occupation, and this article is a fascinating insight into Danish aircrew and their allegiances. There is also information on the shoulder flashes of other Allied countries.
Photograph: Danish National Museum, FHM-204138.