2/11/2012: Redid the shield according to my new standards.
The lesser coat of arms of the Holy Britannian Empire, as I imagine them to be, based on the arms given on Britannia's flag and those of Great Britain as Elizabeth III left it. Sunrise apparently decided to ignore butterflies, thus so shall I. The lesser version is used by HIM Government, the Armed Forces and on the flag of the Realm.
Sable, a bordure Or, a lion Or and a serpent Vert with armaments Gules intertwined and fighting. Above the Crown Imperial proper.
Code Geass and Britannia (C) Sunrise, Bandai and CLAMP.
Ah but that's a Cartouche around the shield if I see it rightly, the crown is still resting on top of the shield above the Bordure in front of the Cartouche.