protocol SegueDelegate {
    func runSegue(identifier: String)
}

class SignUpView: UIView {
    var delegate: SegueDelegate?

    @IBAction func signUp(sender: AnyObject) {
        delegate?.runSegue("goToMainPage")
    }
}


-----------

class WelcomeViewController: UIViewController, SegueDelegate {

    var a = SignUpView()

    override func viewDidLoad() {
        super.viewDidLoad()
        a.delegate = self
    }

    func runSegue(identifier: String) {
        self.performSegueWithIdentifier(identifier, sender: self)
    }