Julia Felsenthal in Slate:
Slate tech columnist Farhad Manjoo argued recently that the fax machine lives on largely because of our attachment to the written signature. Manjoo's observation piqued the Explainer's curiosity: When did scribbling your name on a piece of paper become a means of authentication?
A long time ago. Signatures on written transactions have been customary in Jewish communities since about the second century and among Muslims since the Hegira (the migration of Muhammad and his followers to Medina) in 622. In Europe, the signature dates to the sixth century. But it didn't catch on widely there for another thousand-odd years, until the 16th and 17th centuries, when education and literacy were on the rise and more agreements were made in writing. In England, the 1677 Statute of Frauds—which stipulated that contracts must exist in writing and bear a signature—was pivotal. Signatures became a standard form of validating agreements—a practice that was also adopted in colonial America.
Between the sixth century, when signatures first appeared, and the 17th century, when signing became standard practice, Europeans used various customs to formalize contracts. Wax seals bearing an impressed or embossed figure were common, particularly among the French, who brought the tradition to England during the Norman invasion. (Seals also appear in the Bible, and to this day sealing, not signing, is standard practice in China, Japan, and Korea.) One popular way to create these impressions was to press a signet ring into beeswax. Signet rings themselves were also used as validation: A king might, for example, dispatch a herald bearing an oral message to a foreign power, and give him the royal signet ring so that the message's recipient would be confident of its origin.