I don't speak Swedish, so,I've had to rely on Google Translate.
The wikipedia entry for Sevärdhet makes reference to it being used as the logo for Riksantikvarieämbetet, the Swedish National Heritage Board. Its website prominently displays the symbol.
Note the breaks in the line, as if it was a knot of rope. It so happens that the Bowen Knot is the principle rival to the Borgholm Castle theory.
So yeah, Susan Kare is just as gullible as I was.