Okay so thats out. Did it denote disc brakes ? The shape is common.
Wheres that G.G. all knowing guy when we need him.
I feel certain the washer was a primative semi-perminent form of post-it note for the assembly workers underneath the car.
Should we be also looking for evendence to prove most of these washers were knocked off during assembly ? No. If we all go feeling around through the crud for broken tack welds we'll all need band-aides.