Aurea smiles at the paper, then nods. I agree with... ah, him. She means Reinholdt. The third word of the fifth line of Sonnet 107. It could be the third letter of the fifth word of each line, spelling out a message, but that theory breaks down by the third line. Furthermore, this is from Shakespeare's Fair Youth series, which is about someone expressing their love for a young man. As we all know, the moon is a symbol of femininity, so it could be a symbol for the author of the inscription. If I saw this in a tomb, I would be on the lookout for any images of a moon.
I think she's over analyzing this.