I do like the simplicity of Crowns. It's been used historically by a number of countries, because it just refers to their monarch. Each kingdom/empire of Elemental would have their own Crowns (with their own sovereign's ugly mug stamped on it), so it would make sense for them all to have the same name.
Then again, I suppose if you want to use a made up name, you can just say it means "Crown" in one of the languages of Elemental.
Hey, speaking of our soveriegn's ugly mugs, it would be a nice touch if somewhere in the GUI (like any sort of economics screen) it showed a little gold coin for your kingdom with your sovereign's image stamped into it. You could just take the image/pose from his info card.
Superficial, I know, but it would be nice.