The Department of Defense (DoD) permits retired officers to use their military titles and status under certain circumstances. Such use is regulated, however, to ensure that the conduct of retired personnel neither discredits the service nor implies that the DoD is endorsing any nonofficial commercial activities.
DoD regulations permit retired officers to use their military titles socially and in connection with commercial activities as long as they don't involve any ethically questionable associations. They’re also not allowed to use their military title in connection with any activity, commercial or otherwise, when such use implies the DoD sponsors or otherwise approves of that activity. Retired officers also may not use their military titles during public appearances in other countries, unless authorized by the theater commander, to prevent other nations from inferring that the U.S. military supports foreign groups or causes not officially sanctioned by the DoD and the U.S. State Department.
Retired officers who accept jobs as federal civil servants after retirement have some further restrictions placed on them, both legal and practical. For example, retired military officer civil servants may not use their military rank as part of a signature block on official correspondence, as their former military standing isn’t relevant to federal civilian policy. When working as a civilian as part of a military command, a retired officer may not answer telephones using his or her retired rank, as doing so would cause confusion in the mind of the caller as to who was taking the call. Common sense also dictates that retired officers working at military commands don’t ask to be called by their retired rank when that rank is senior to other officers in their military/civilian chain of command, especially if that includes the commanding officer.
If retired officers have business cards that include their rank, they must reflect the fact that the officer is retired, as must any social calling cards they have, by including the phrase “(Ret.)” after their rank. The same restriction pertains to retired officers who use their military title or rank to sign personal documents. Finally, retired officers are entitled to wear their uniforms whenever they want, but most choose not to do so except on formal occasions such as military balls or possibly to enlist or commission one of their children or other close relatives. Wearing a uniform in daily activities can cause confusion in the same way as using rank in business or social occasions can.