First, you'll need to wrap this in a promise like:

    .then(function(ob) {
      return notices.signedQs(ob);
    })
    .then(function(signedQueryString) {
      var url = ob.callback_url + '?' + signedQueryString;
    })

Secondly, note how there is no need to url encode the object.
This should just be ``ob.callback_url + '?' + notices.signedQs(params)``