Actually, if that was the real wording they used 'on signup', it's not misleading, it's a bald-faced lie, assuming they will not honor that statement. It doesn't say any of that other shit, if it says 'on signup' then that's all that is required. It doesn't say 'by the way, you only get 20% on sign-up, the rest is just bullshit'.
Again, I haven't seen the ad myself but if Danny is accurate, I'd have no problem calling them liars.