If you press the minus button (-), you'll get a different set of options than the usual Save and End and Continue Playing options you'd get when you're offline (or if your gates are open but no one is there). If you have visitors, you can view who they are by selecting the view passport option. If your gates are open but no one is there, that option won't be visible, but you'll be able to tell your gate is open either by attempting to change a pattern (which you can't do while the gate is open) or if you just visit your airport. Hope this helped!