What do the Footnotes in Gene Wolfe's 'The Urth of the New Sun' refer to?

I just finished reading Gene Wolfe's 'The Urth of the New Sun'. Several times throughout the book, I noticed at the bottom of the page what appears to be a footnote reference. It looked like this:

T.U.O.T.N.S - 12

The number starts at 1 and goes up to around 20 or so. The note is always on the right hand page at the bottom.

I am totally perplexed. I couldn't find references to this anywhere after exstensive googling. To make this mystery even more frustrating, I just started reading another of his books - 'The Devil in a Forest', and I've noticed similar notes again, 'T.D.I.A.F - C' (Letters instead of numbers this time).

Does anyone have any clue what these mean or link to?