It (supposedly) was the symbol of the Rurikovich dynasty that ruled Kievan Rus and Novgorod (and other feudal states in western Russia that I cannot recall) during the Middle Ages. Now it’s mostly used by Ukranian nationalists, banderites and other fascists. IIRC it was also used by anti-soviet reactionaries and fascists in Ukraine during the 20th century
Interesting! I had not heard that theory before. It’s possible that they adopted such a practice, they were “vikings” after all