Jim,
I think you are right. It was drilled and attached to the fender tag (under it) you can see the rust line vs the paint where it was covered up.
Need to check to see when it was built. Drunk and hungover factory worker could not bend over to attach to back seat springs so they screwed it under hood I guess.
Weird thing is it was painted possibly bent up in the air because the inner fender does not show a line where it was laid down.
I would like to find the meaning of it just for curiosity sake.