footer notations of a*, b*, c*?

Factual Questions
1

In a newly offered Vintage publication of Seven Pillars of Wisdom, there a notations on the bottom left of some pages as my title suggests: a*, b*, etc. through to y*.

Does anyone know what those might indicate? There is no reference to those markers in the index or two appendices. Is it a reference that Lawrence may have made? If so, why did the publisher add the notation without explanation?

Thanks, as always,
Heckiity

2

How often do the markings occur? Is it every 16 or 32 pages, or some other even number? It might be a count of the signatures. (For those who don’t know: Books are printed on biiig sheets of paper that are then folded up. Each group of pages that results from this folding is called a signature. The signatures are then sewn or glued together, the folded ends are trimmed off, and a cover is attached. Wikipedia description)