Back when I had Halo 2, my emblem used to be this:

To me, it looked like the shape of a Hammer head dragon.
If you wanna make it, use:
Vortex emblem.
Double Half Circles background.
Make player color 1, and emblem color 1 the same, and player color 2, and emblem color 2 the same.
(Halo 2 Emblem Generator)
The emblem won't show up next to the box. Copy the "Image" code, and paste it in the URL bar.