John
Separated this off the other thread to make it its own thread
This is not a common mark IMHO and from my research and can only be found an a handful of original hoods, rather than all cars. May have indicated a problem, issue or the start or end of a group of cars.
Earliest car I've seen them on is a Nov 64 San Jose if I recall correctly and the latest was built during 67 production there. Similar mark can also found on the trunk lid in 68 but these might be unrelated though may be used for a similar purpose. Just as rare to find them there as under the hood. May be the same guy/worker for all of these (different letters and marking used) since the hand writing appears to be the same or very similar on many of the examples IMHO
So with these findings consider that this is likely a late assembly line mark (after the drivetrain, suspension and body has been basically all assembled) and the markings are placed high up on the trunk or hood so that they could be seen from a distance when one or both are fully open. Basically the vast majority of the time they are moving on the line
Just my thoughts so far on the subject