Honorific
If the person used the prefixes to refer to himself, that was regarded as low behaviour, egotistical. The one exception was the medical doctorate in the UK. A medical doctor could described himself as Dr. Brown, and he would be understood as being a medic. There were originally no PhDs awarded in British universities, and they were uncommon until after the Second World War. Civil servants signed letters "Your obedient servant" to emphasize their intermediate role between government and the people, or between Parliament and the people.