I’ve noticed that my KJV Bible occasionally has odd letters and numbers low down in the corner of certain pages. What do these denote?

Some of our older Bibles, such as Concord, Turquoise and Cameo date from the early 20th century, when much of the collation work was done by hand and these ‘signature marks’ helped with the correct gathering sequence of the Bible. They are retained in these facsimile legacy editions for historical interest.