Factory numbers inside rocker panels? 1984

While sanding down a somewhat early built '84 for paint, (about 4000 VIN)  I took the right side rocker panel off and found these numbers drawn in pink (or maybe way back then it was red and has faded) marker on the inside about mid way down. Does anybody know what they might mean?

 Looks like 28  then a dash, and then 15 x 7 to me.

Guess the picture didn't make it...

Here is the driver side rocker panel numbers. I thought these numbers might be real close to the pass side panel picture above since the car went down the line and surely both got put on on the same day, but?? Ideas anybody?

No idea....but that doesn't look like an "X"...looks like a scribbled "4".