This simbol was one of the weapons of the Kotromanic family. The family weapon was he black lion and a striped background. But the banner of the kingdom, without doubt has been the fleur des lilles, 6 of them. Thhis banner appears not only on coins, but what is more important, also on all the official stamps with which the kings signed documents as a banner of the kingdom.
For example this one of king Dabisa:
We can see right of him the banner of Serbia and left of him the banner of Bosnia and holding this same banner in his hand when going to battle as a Bosnian king. A similar stamo the first Bosnian king Tvrtko I Kotromanic has:
You can see again the Bosnian flag and the Serbian flag. This weapon which you used is never visible as a banner of whole of the kingdom like the fleur des lilles are.