I am a retired attorney, I am in good standing, but as a retired attorney I cannot practice law. When can I use "attorney" or "attorney at law"? Would it be ethical? Can I still sign my name with "Esquire" after it? After all, once a retired Navy captain, always a captain.

The use of Esquire or Esq. after your name is acceptable. Strictly speaking, it’s not an etiquette faux pas to use the word “attorney” or the phrase “attorney at law” on your letterhead. However, by doing so you run the risk that people will think you are still practicing and they might solicit you for work. The same would be true on your return address. Because you indicate you cannot practice law anymore, you should consult your state’s ethics rules.