Esquire (abbreviated Esq.) is a title of British origin, descended from the position squire, an apprentice to a knight. In late 20th century America, an Esquire was a title given to men or women who practiced law, as well as some diplomats. In the United Kingdom at that time, the title referred to bankers.
Bill S. Preston, Esq. added the title postnomially to his name, even as a high school student and without ever practicing law. He also referred to his grandmother as Granny S. Preston, Esq., although it was unknown if she was a lawyer or diplomat.