The letters printed in the tail margin of the first leaf (at least) of each gathering or section of a book, as a guide to the binder in assembling them correctly. Signatures normally run from A to Z, omitting, by convention, J and U, which in earlier days were capitalised as I and V, and also W. If the whole alphabet has been run through, they usually proceed to AA, BB, or Aa, Bb, etc. These are commonly indicated in bibliographical descriptions as 2A, 2B, 3A, 3B, etc. When, as an alternative, a single-letter alphabet is simply repeated, it is convenient to indicate the subsequent alphabets as 2A, 3A, 2B, 3B, etc.
Swedish: Signerat exemplar