How to pass properties from One controller to another in ember without involving route's setupController?

In simplest cases you can inject one controller into another:

// app/controllers/signup.js

import Controller, { inject as controller } from '@ember/controller';

export default Controller.extend({
  login: controller('login'),

  signup() {
    // Do some requests to create new user

    // And then set properties on login controller
    this.login.set('formData', {
      email: this.get('formData.email'),
      password: this.get('formData.password'),
    });
  }
});

For something more complex, services are good.