Board Thread:Questions and Answers/@comment-1189400-20181110124135/@comment-1189400-20181215162848

I think at least for the First Bulgarian Empire it's unacceptable to have as a flag the coat of arms of its successor state's last ruler whose royal status isn't even proven and which coat of arms was only attested centuries after that ruler's death.

I've also discovered there's also showing "Koutragon the Bulgarian" (considered to be Khan Omourtag) holding a shield with a brownish-red wing-like symbol on white (I would have said horse tail or maybe wolf's tail, seeing as Boris I, Omourtag's grandson, gets berated by the Constantinople patriarch for using a horse tail as a banner, but this here doesn't quite look like the tails of any  in the chronicle's minatures). Unlike other shield designs which are depicted on many armies in that chronicle, this shield is unique un the Madrid Skylitzes.

So from that standpoint, in the absence of an actual flag, this symbol sounds like a better design.