I've had this for years, and honestly have never seen another. I'm not a cowboy but some of you guys in cattle country may recognize it.
It's a Cowboy Hat Holder. Mounts usually on the interior trim above the inside rear view mirror at the top of the windshield. The spring allows it to pull down, put the hat in upside down, and the spring holds it up in place while you drive.
Believe it's a hat holder to hold your ten gallon Stetson while driving. Attached to the roof of your pickup to hold your hat with the brim up, The crown pointing downward through the ring. Ted
I'm not an old timer and I know what they are. They can still be found at western wear shops. Actually, I was thinking of getting one for my truck to hold my shade hat for the shows.
When I went to work for Carquest Auto Parts here in Houston some years ago, the 90s, these and rifle racks etc. were being stocked in their stores. Can't remember the manufacturer but they were dropped by the mid-90s.