On the origins of "Esquire" (or "Esq.") as an honorific for lawyers:
The word itself derives from Old French, and in turn from Latin, where it means something like “shield-holder.” In the 1200s and 1300s in England, a variety of languages were used, so such figures might be referred to as the … French escuier, which became “esquire.” These terms all refer to roughly similar people. This role was generally considered moderately prestigious for young men of some wealth, but at its core it was a service job. You carry a knight’s stuff, tend to his horses, that kind of thing. “Esquire” and “squire” were names for the same gig for a few hundred years.
This post additionally reveals that the bars of California, Arizona, and the District of Columbia have admonished or penalized non-lawyers appending "Esquire" (or "Esq.") to their names, as this may "erroneously signal the capacity to practice law."
In 1363, the esquire’s place as a respectable social rank was codified in the Sumptuary Laws, which were essentially a huge list of what different groups of people could and could not wear. That list included esquires as a social group …. This was the same time that the idea of a gentry emerged in England: people who are not noble, but certainly not peasants, either. ….
So esquire had come to suggest moderate respectability with a dash of prestigious servitude. By the 1500s, knighthood no longer necessarily had any connection to soldiering and had begun to be used simply as an honorific, a nice title a sovereign could hand out to pals. A similar process occurred for esquire, and divorced it from its roots. By 1586, a writer named John Ferne had already described the term as basically meaningless and kind of annoying, used by rich guys who wanted to seem noble-adjacent.
Successive writers tried to pin down what it actually meant, with no great success. Ferne, who was himself also a lawyer, noted that it was often used by those in the legal profession.
(photo: Bill S. Preston, Esq.)