Leaf through “Mechanic’s Companion,” and you’ll find a signature at the top of some of the pages. Those are, I assume, the signature of the original owner (J. Hildebrand?) of the book I scanned to produce my printing.
So why didn’t I clean those up (i.e. erase them) as I was working on all the foxing? Well, I think they’re charming – and they don’t interfere with legibility, so I left them.
Today, it is more common to use a bookplate or sign one’s copy in the front of ones books to identify the owner. But it was fairly typical at one time to sign multiple times, and on the same pages in every book in one’s library. That way, if the cover and end sheets were damaged or removed, one could turn to the chosen pages and know to whom it belonged. A borrower (or thief) would be less likely to remove pages with necessary information!