The 'C' Rock
One particular rock somehow has a letter 'C' printed on it from Apollo 16 mission. This was marked to show where an astronaut should be standing as actors have on a stage when performing.
Oh Really? Yes one picture does seem to show a letter C. But this particular picture is a third generation copy after the original negative has been through a photographic enlarger - prone to dust and hair infection if not careful. Such items will show up as a silhouette.
The Original Image
Third Generation Copy
The left picture is direct from the original. The right is a third generation copy. Note the quality of the image of the original. The contrast always increases on copies produced via film. So the 'C' is just a fine hair laid on the copied image from a dusty darkroom; nothing more.
Most of the published images seen in books etc are not from the original film taken on the moon; they are priceless and are handled to an absolute minimum. Images you see in print are often 2nd, 3rd, or even 4th generation copies.
The entire Apollo film archive has now been digitised by high quality scanners to remove this problem of contamination by dust & hairs and decreased quality. Such facilities were not available when this 'C' Rock picture was published.