How to tell if a Retina MacBook Pro has gone to sleep when the lid is closed? When I shut the lid on my Retina MacBook Pro (2014), how can I tell it's gone to sleep correctly?

On my previous MacBook Pro (~2008), the fans were audible, and there was a sleeping LED indicator in the lid latch that changed from "on" to "pulsing" when it was asleep. I used this as an "okay" sign to put it in the laptop bag.

Is there anyway to tell if a more recent MacBook Pro is asleep? I can't hear the fan most of the time, and I can't see any externally visible indicator lights that would indicate it's status.

I'm worried if it hasn't sleep correctly when I close the lid (occasionally this would happen with my old laptop) it will overheat when I put it in my bag.
It won't just overheat in its bag, but will also quickly drain its battery.
I always press the power button for about 1 to 2 seconds before closing the lid. The screen will go dark when you release. If you hold it too long, a dialog will come up asking if you want to sleep or shutdown. Choose wisely.