Of course the first time they ban or kick someone everyone will know they're admin.
Maybe I should add secret ban and kick commands too.
Just make it look like they disconnected, and don't display a ban message to them I guess. Don't know how it would work if they try to rejoin.
But if you do add secret ban/kick commands, let other admins use them. If it would be possible, maybe it so that a message is displayed to Admin/SA/Host when someone is secret banned, so admins can't ban people without you knowing.