I can't either. I downloaded the image full size (3088 x 4216 px), looked it over, didn't find anything. To try to bring out any writing that was obscured by the uneven lighting I started experimenting: Image > Adjustments > Invert, then Image > Adjustments > Curves using a curve to even out the lighting and accentuate any scratches, zoom to 200%, looked it over, no joy, then Image > Adjustments > Posterize, I'm still not seeing it.
Is this photo identical to the one that was used in the viewing experiment?