We seem to have a letter 'C' on this rock. But this is a third generation copy. During the process at some point, a fine hair laid on the negative film and was silhouetted onto the rock. Observe the original picture at the bottom. The quality is far better showing it's from the original slide and not a copy of a copy... no letter 'C'.  More detail in the book.

the 'c' rock

Copyright © Astronomy Roadshow All rights Reserved