Yet another detail shot of that Peter Lombard text I've been working with (which I now believe to date from the first half of the 12th century, not the 13th as previously thought).

This mark at the bottom of the page that looks like a numeral "1" in a sunburst confused me at first, but I found some reference to it. It turns out these are probably scribe's marks to denote which scribe was to be paid for which section of a book!

As always, producing books was an industry and during the Middle Ages, scribes both within and outside the monasteries made their living copying popular titles.