How do I find which side on a spinner is facing up?

Hi I am trying to make one of those spinners with 5 sides, so 72 degrees each, which I apply a random torque to, and then get a random side to be picked, which is the side that is facing up.

I can't figure out how to find which side is facing up, as I am relatively new to unity. I tried using the transform.rotation.z as the spinner is rotating around the z axis but this did not work. Any help would be appreciated. Here is an example of what I am talking about: