I think for the user it doesn't matter if he's already signed out or not. Does it? I would simply do something like this:

```ruby
def verify_signed_out_user
  destroy_session if user_already_signed_out?
end
```

Where `destroy_session` would be exactly this code: https://github.com/plataformatec/devise/blob/sign_out_not_logged_in_user/app/controllers/devise/sessions_controller.rb#L27-L35 shared in between the filter and the action.