Looks like there might already be a jack instruction label on the trunk lid of this Charger. I know this is the Hamtramck assembly plant but as I mentioned I'm pretty sure the recipe or procedure for Chrysler assembling vehicles during that time did not vary enough to make too many differences in the process. You can see the broadcast sheet for the interior (seat color, level) in the usual seat back and note there is no driveline, engine, etc., thus no wheels or tires. With the height of the car at this point the spare tire would be difficult to place into the trunk so was it in there already at this point or installed farther down the line. I'm starting to think that it may be an inspector's mark as noted confirming the correct spare was in place. Check out the end of the assembly line final control with trunk lid open, trunk lid closed, car being moved off the line. Was the spare and trunk inspected and a mark placed on the lid to confirm anything...................we're all just guessing