I don't know what the recommended size is since Gravatar accepts all sizes.
I'd love to have one with a skull/soldier and guns on it, in a black background (coulour of skull doesn't matter). My username also has to be on it (Athemoe) and the word "Anthrax", Anthrax has to be bigger than my username, since it's more important. The colours of the names can be red. You can choose your own colours though, if it doesn't work out.This is an example of a fellow platoon member:
Spoiler
