If you're in New Jersey and take the turnpike, that slot will hold your toll card. I put one under my visor years ago and it blew out the window. I had to pay full price of the toll from the furthest point to that stop.
If you have a hitch, my wife and I use this carrier we bought at Walmart online.
https://www.walmart.com/ip/Fultyme-RV-1300-Hitch-Mount-2-Bike-Rack-200-lbs-Capacity/692554514