Tommy says…

 I’d thought that Esq. was the same as Mr., but it turns out it (technically) isn’t. According to http://en.wikipedia.org/wiki/Esquire, esquires are the lowest title of dignity above gentlemen.

So are you an esquire? You are, if…

• You are the oldest son/grandson etc of a knight, or the son/grandson etc of a peer;
• You are a judge;
• You are a sheriff, JP, QC, or just a barrister;
• You have a degree from Cambridge or Oxford;
• You have a bachelor’s degree in Law, Divinity, or Medicine;
• You are a high ranking military officer, or
• The Queen calls you an esquire.

This is the (complicated) British usage. In American usage, if you are a lawyer, you are an esquire. So, who’s an esquire?