How to detect if WSFederation session has expired or ended?

See more:

C#

MVC

I have a several methods in controller:

public ActionResult Issue()
{
    var message = WSFederationMessage.CreateFromUri(HttpContext.Request.Url);

    // sign in
    var signinMessage = message as SignInRequestMessage;
    if (signinMessage != null)
    {
        return ProcessWSFederationSignIn(signinMessage, ClaimsPrincipal.Current);
    }

    // sign out
    var signoutMessage = message as SignOutRequestMessage;
    if (signoutMessage != null)
    {
        return ProcessWSFederationSignOut(signoutMessage);
    }

    return View("Error");
}

And the most valuable for me in this question:

private ActionResult ProcessWSFederationSignOut(SignOutRequestMessage message)
{
    FederatedAuthentication.SessionAuthenticationModule.SignOut();

    var mgr = new SignInSessionsManager(HttpContext, _cookieName);

    // check for return url
    if (!string.IsNullOrWhiteSpace(message.Reply) && mgr.ContainsUrl(message.Reply))
    {
        ViewBag.ReturnUrl = message.Reply;
    }

    return View("Signout");
}

All works fine, but, there are interesting moment. This thing works in both cases, if I ended session by myself, or session simply expired. Its fine but actually, I need to tell the difference between those cases, write in ViewBag something like "You are singed out" or "Session expired" depends on result and show it oy the View.

Is there are some kind of way to detect session expired situations or should it be something different?

P.S Sorry for my bad English.