McGrath of Harlow:

Somehow "esquire" has come IN SOME PARTS OF THE UNITED STATES to be a particular honorific for a lawyer. Not everywhere. Here in Indiana one sees it, but not so very often.

Actually, it means approximately the same as "Mister", namely that the individual is a gentleman (in the class sense, not the behavior sense). Thus one could well address a letter to me (a non-lawyer), perhaps, as David Oesterreich, Esq. But never Mr. David Oesterreich, Esq., regardless of legal qualifications.

I am also somewhat bemused and maybe amused by "Shirley Ann Jones, Esq.", which is a usage I see often in these days when woman lawyers are a dime a dozen. It's like saying "Mr. Shirley Ann Jones".