O Esquire is an honorary degree that is placed after the name of a practicing attorney. Practicing attorneys are those who have approved one from a state (or from Washington, D.C.). I've never heard of a prefix (assuming you're referring to the honorific anteponym) that is used to refer to lawyers the way Doctor or Professor is used. However, it is common for U.S.
lawyers to use the deferred honorary title Esquire (such as Esq. No one ever refers to himself as Esq, only to others. It's not a legal designation: anyone can call anyone, or themselves, Esq.