The term Esquire, or Esq. for short was, and still is to a lesser extent, used in correspondence here in the UK.
In the early part of the last century it was often used by the trade (of any description, not just gun makers) when addressing correspondence to their customers. It is less usual these days, but then so are letters!
Two hundred odd years ago it used only to be used when addressing someone of a certain rank or standing in society. I forget all of the criteria but do know that anyone of the rank of captain or above was entitled to be referred to as Esquire, because I met that particular bar!
The convention is that it is used after the persons name only. It would be incorrect to preface a name with Mr, Dr, Capt or whatever, when using Esq.
Tim
