"Sources are scant about the Union of Kalmar flag. These are a couple of brief passages of text. There is no pictorial evidence attesting to the Union flag from the time of the Union of Kalmar (though some authors point to heraldic evidence for a red union cross) and definitely no surviving flag. A flag seen by Hugh Watkins in a museum showing a red Scandinavian cross on a yellow field is a recreation of what is thought to have been the union flag. (Jan Oskar Engene, 11 February 2004)
"What remains of evidence is two letters from 1430 in which King Erik orders the priests of Vadstena and Kalmar to wear the "banner of the realms" on their robes. The banner is described as 'a red cross on top of a yellow field.'" (Jan Oskar Engene, 16 February 2004)
crwflags.com
