I remembered to look on my '69 RR - St. Louis car, SPD 2/12/69, unmolested 17,800-mile original car.
Fender bolts have a raised G in their centers, a raised L inside the G, and a single raised line @ 12:00, 6:00, and 9:00 positions.
I'm used to seeing a raised anchor, or a couple of concentric circles with (IIRC) short lines radiating outward on my '68 & '69 B-bodies.
Hope that helps.