Darrowmere, I have a sample of the symbols. I know you wanted the Horde (or Durotar actually) to be black on red, but I think this "3d metal" version looks better, more WoWish Id say. These samples are around twice the size what the symbols would be in game - campaign, so there would be very little detail lost.
Still, if you prefer the symbols to be flat and solid colour, then you can have them that way. Just wanted to show you what I think could look better. Also, many symbols (in the lore sources) are often presented with that 3d look as sort of 3d devices over some background, so it's easier to adapt them like that cause when made flat they just look so ... plain. Another thing I'm not sure is what kind of background or shield you want for the symbols, something like I show here or different? I can only say that anything without a fat border/outline is good because it gives more room for the symbol itself. I like round symbols cause they are pretty universal and uniformal, but if you want different, let me know. They can even be different shapes for different factions, though that can get little confusing, dunno.
Tell me what you think about all I said.