Yeah, looks good. But I think RxJava also fines in this case, something like this:

if (response.getCode() == 403) {
  subscriber.onError(new Exception(…));
} else {
  subscriber.onNext(respone);
}

observable.subscribe(new Action1<Respone>() {
  @Override public void call(Respone respone) {
    // do stuff here
  }
}, new Action1<Throwable>() {
  @Override public void call(Throwable throwable) {
    // show error
  }
});