just to put another fly in the ointment, here's the imperial byzantine flag:
i note the russian and austrian ones always show both eagles wearing crowns as well as the large one above them all, but the byzantine one, and the sword's one do not....also no breast shield on the sword or the eastern roman flag.
the sword is a bit new to be byzantine tho.....
a quick troll around for bicephalous eagles also shows that the holy roman empire used it with either nothing in the claws, a sword in the right, orb in the left, or a sceptre in the right, or even a sword in both claws.....the eagles heads normally uncrowned, but occasionally with a background ring of some sort, like the sword.
maybe one of the electors (who were mostly german) issued similar swords and one of his soldiers doodled a crude image on his blade whilst having nothing better to do (except hiding from his sergeant of course).
the HRE never actually died out......it's still around
(the current emperor is Emperor Charles VIII) and it's college of heraldry is even on line.....
http://www.imperialcollegeofheraldry.org/
bicephalous eagles were also used by many of the balkan states and even greece. albania has it on their flag, serbia and montenegro also have used this symbol, sometimes with the orb and sword or sceptre.
the possibilities seem endless.....