There isn't one
Nothing wrong with extension .. only i have never have good experience with using extensions when updating my forums so my new forum want extension free
You will have even more bad experiences updating your boards if you start changing core code in preference to using extensions
Ok... i properly thinking of mods.. ill have to look into extension
ok, I'll bite, what group are you going to use for this? you can't use the guest group because if someone is registered then they would not be in the guest group. you can't use the registered usergroup because they either will or won't choose an avatar.