There is a thread in the FutureMyth forum that discusses some of the items included in GameSpy's latest Myth III article, which includes new screenshots and movies of character animations. A bit down in the thread, Orlando the Axe says that iggy popped claims that players will be able to design their own logos for use online. Santa's Head has a tip for you:

For those of you wanting to plan ahead, the logos will need to be 64x64 RGBA files. There are a few other particulars, but that will get you going for now.

I believe this is something that Bungie had planned to include in Myth II, but were not able to. The more customization allowed for the player, the better.