The Smithsonian offers a detailed look of why and how a book published in 1632 England ended up with a cipher on its cover:

This volume, bound in fine leather, is the only other known to be marked with her cipher; designed with the aid of a bookbinder or perhaps by Wroth alone, the cipher must have been intended to remind Herbert of their love, for the jumbled letters unscramble to spell the fictional lovers’ names, “Pamphilia” and “Amphilanthus.”