I was looking for an insignia to put on the Red Devils when they get here.

Here is my first idea:

If you're going for versimmilitude (but why would you with zombies and gorillas?) I believe the symbol used in WWII was this:

These folks have the decals of this patch you mention:

http://homepage.mac.com/brentdietrich/companyB_decals.htm

However, I want something more like the devil face, and I will use the correct patch on the shoulders.