Road Runner Nest

Hello all, Here is something I've been wondering about. I have a 71 Road Runner and behind the rear upper seat (passenger side) there is the body paint code written in marker. None of my other Mopars have this nor have i seen it in any publication or on the net. I imagine it was placed there when it was going down the line so it wasn't confused with another car. My car is (FJ6) sassy grass with a (X9)black transverse stripe. J6 and X9. I'm confused why this was placed there if the car was built to the build sheet specks. My car came out of the Windsor Ontario plant if that helps any.

Looks to me. Like one of those, "I'm gonna mess with some future owner's head. When they take this car apart someday," ha, ha! Seems to be working.

From time to time I have found similar writing ,body color behind headlight, ride height on inner fender ect.
Probably just line workers making notes.
Cool little hiden number though.
Dave