Mary Elizabeth "Mimi" Carr had no trouble deciding that she would sign her name with an "Esquire" at the end, but other CVESD teacher-lawyers aren't so sure. Here's some authoritative information for them.
The Straight Dope Science Advisory Board says:
Now you might ask: what allows one to use this title? Is there a ceremony? Is it conferred by a university? Is it just some affectation that snob-nosed folks use? Can I be Joe Blow, Esq. just because I like the ring to it? Or do I need to get authorization, and if so from what? from where?
The answer is that any snob in the world (or at least in the U.S.) can use the title...
Now of course in England there's this whole business about hereditary nobility and getting knighted and all that, so it might be a little risky to start calling yourself esquire there. (Although what's going to happen? The Snob Cops arrest you?)
But we're not in England, we're in America! The land of the free, the home of the brave! You can call yourself anything you want ... although you do take the risk that you will be thought a snooty jerk.
Since this has never bothered lawyers, they have gotten into the habit of calling each other esquire. This is a little like elected officials addressing each other as "honorable," which to me seems a classic case of advertising something after it's gone. But I digress.
Among lawyers, it's thought pretentious if you sign yourself "Esq." in written communications but you are supposed to dignify other lawyers with the appellation... even if you never saw the inside of a law school there's nothing to prevent you from calling yourself esquire ... except the fact that you might be thought a lawyer.