Possibly what the Keyblade looks like?

[5 Kings of Twilight]

That could be what DFKWU's keyblade looks like.
For those thinking it looks like Bond of Flames, it looks nothing like it.
I don't think it symbolizes anything.

 

[Sunset Horizons]

That's an interesting spirte. I wouldn't go as far as naming the blade, but I do like it.

 

[Relik]

5 kings is right, it looks nothing like Bond of Flames and thankfully should have no connection to Axel. Just like the one knight who has a different keyblade before picking up the keyblade that looks like Sora's