Same goes for me being 67 and I bought the Dark Horse so I can have some fun driving in it as much as I can before I die! I had the Cobra 2003 convertible and had so much fun driving and tinkering with SVT supercharger! Reminiscing the old times with the current Dark Horse!
I agree with it as “wrinkles” of 4 or 5 identified when blowing the picture up and see it! Maybe that would help identify whether prints are like that on the buckle itself or not!
Looks like the seat belt buckle got caught in between the door, sometimes when getting out the strap gets tangled and doesn't bring the buckle all the way up and gets out and closed the door without looking at the seat belt is properly unslacked up! Not sure from the picture where this happened...