class TrackedViewController : UIViewController {

    static var currentViewController: TrackedViewController?
    static var previousViewController: TrackedViewController?

    override viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        TrackedViewController.previousViewController = currentViewController
        TrackedViewController.currentViewController = self
    }

}

if let myController = TrackedViewController.previousViewController as? MyViewController {
    // Code here if the screen was reached from MyViewController instance
}

class TrackedViewController : UIViewController {

    static var currentViewControllerID: String?
    static var previousViewControllerID: String?

    override viewWillAppear(animated: Bool) {
        super.viewWillAppear(animated)
        TrackedViewController.previousViewController = currentViewController
        TrackedViewController.currentViewController = self.screenIdentifier
    }
    var screenIdentifier: String {
        return "defaultScreen" // TODO: every view controller must override this method and have unique identifier
    }
}