Hi. Sorry for taking so long, we were discussing about this.
Paying for ads removal only removes the 3rd-party ads. For the "Powered by Nabble" (which we shortened so it bothers less) you can use CSS to hide it but it may become a premium feature only in the future and we may restore it at any time. In this case, to keep this modification from that moment on, it would require that you become a premium user.
Nabble staff. We never ask for passwords.