Maybe you need at least a specific number of +rep then you can, thats what it was like in some other game forums, but probz here they havn't modified forum to allow animated avatars and sigs yet.
Tribal Wars doesn't allow animated avatars or signatures
I think it's because they're servers can't handle it?
Otherwise there should be no problem moderating it... I mean just how many people post here? It'd be easier to moderate than moderating individual posts (More posts than people).