You sign yourself as "MD" which I take to mean that you're a graduate of a medical school.Assuming further that you're licensed to practice medicine somewhere in the US would you still be allowed to bill yourself as "MD" if your license were to expire,be suspended or be revoked? I obviously understand that you wouldn't be allowed to *practice* medicine in any such situation.
MD means you attended a Med School in the Allopathic tradition. DO is for Osteopaths. Naturopaths and homeopaths have no initials after their name (I am almost certain).