Follow up with Mukul More at http://stackoverflow.com/a/23891481/1271826

ChildViewController.swift

import UIKit

class ChildViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        print("ChildViewController.viewDidLoad")
    }

}

ViewController.swift

import UIKit

class ViewController: UIViewController {

    // in Swift 3
    
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        print("ParentViewController.prepareForSegue: \(segue.identifier ?? "")")
    }

    // or in Swift 2
    //
    // override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    //     print("ParentViewController.prepareForSegue: \(segue.identifier ?? "")")
    // }

}

When I did this with embed segue (i.e. I dragged "container view" from object library onto a storyboard scene, the output was:

ParentViewController.prepareForSegue: EmbedSegue
ChildViewController.viewDidLoad