[Broadcast Subscribers] gets the Bitmessage Icon for identification. This is hard-coded now, I would favour to put [Broadcast Subscribers] as a fixed item into the Address Book, so you can set an avatar as soon as i implement avatars.
Still no options yet: There will be an option to disable Identicons and Avatars separately. Another option will be for the suffix (to mimic adresses like "BM-...@bitmessage.ch" or to add a personal "salt" to prevent identicon attacks where someone creates an address with an identicon that looks alike the one of a known address). Also, identicon size (coupled with row height) should be available, but is of low priority.
Next step (after the settings) is to load specific avatars for each address.