"I would willingly have gone with thee into the forest, and signed my name in the Black Man’s book too, and that with my own blood"
Witches exchanging the Bible for the devil's book
Public DomainWitches exchanging the Bible for the devil's book - Credit: From G. P. Guaccius' Compendium Maleficarum. Milan, 1626.

Puritan belief had it that in order to become a witch, one had to formally sign one’s name in the devil’s book. Through this signature, the witch denounced God and pledged his or her soul to Satan. The latter would then confer supernatural powers upon his new comrade in the war against God. During the Salem witch trials, a confession of having signed the devil’s book was considered key evidence. Read an account of one such confession, that of Mercy Short, here.