E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Letters at the Foot of a Page.
Printers affix a letter to the first page of each sheet; these letters are called signatures. They begin with B, and sometimes, but not always, omit J, V, W. A is reserved for the title and preface. After Z, the alphabet is used doublethus, A A or 2Aand then trebled, quadrupled, etc., as necessity demands. Sometimes figures, 1, 2, 3, etc., are used instead of letters. (See SHEET.)