Ive found markings on those panels on quite a few cars. And they've all been written on after paint, unlike the firewall markings. Found "GR" on the Gold RS Z Im building. I never really understood why there would be markings on those panels, since they really arent specific to any options.
The emblem suggestion is interesting, but there arent any emblems on that panel. Unless maybe it was written after it was attached to the fender?