Devise disable signup

routes

devise_for :users, :skip => [:registrations] 
as :user do
  get 'users/edit' => 'devise/registrations#edit', :as => 'edit_user_registration'
  put 'users' => 'devise/registrations#update', :as => 'user_registration'
end

# And then modify the app/views/devise/shared/_links.erb

I guess it depends on what you're editing about them. Removing registerable still allows existing users to change their passwords and some other basic stuff, just not any stuff you have in registration like their email address or cancelling an account.

I agree with @CoryFoy, removing :registerable from the model makes the sign up link not to be rendered in the form and the route not being generated.