Here is a question, on picture 24 of 55 in the Virginia Mustang blog. Why does the core support have a dot of yellow paint in the middle of the top part? Does that yellow paint tell someone on the assembly line something as it is being built?
Yes it does by yours may not have had the same mark. Seen allot without it.
The purpose of just about all markings is to get someones attention, let them know something quickly about the car coming to their station, indicate something has been completed, inspected, checked, paint color to use................ Shifts and workers assigned the task of marking the bodies would sometimes differ but each had their method. These may seem random until you see enough of them and patterns/habits often become apparent
And you will also notice the writing on the radiator support (again instructions or indicators to other workers on the line) they are covered by engine compartment black when the car is painted not over it as you see in some "restoration"
Did the same (different writing and of course plant & year) on my Boss about three years back