That is called a footman's loop. It dates back to the original WWII Jeeps and is where you route a strap to tie down your windshield when folded forward (its rarely done with a JK). If you look on the inside of your windshield frame just above the mirror, you will see another loop for the other end of the strap. Also, you will see 2 rubber bumpers on the hood, they are what the windshield would rest on.
Oh, and by the way:
Welcome to the forum!
Click here for helpful tips for newcomers