Signing a letter

If one's title contains professional credentials; e.g. Dr., Prof. or knighted under a British system - Sir so-and-so. Would they put this after they have signed? Your sincerely, sign, Sir Andrew Smith or should it remain Andrew Smith or bracketed Andrew Smith (Sir)?

[Casiopea]

Is it a business letter? According to the information on this site,

"Your full typewritten name and designation (on separate lines) should appear beneath your handwritten signature."

All the best.

[Ouisch]

One wouldn't use his professional honorific in his typewritten signature. That is, he wouldn't put "Dr. John Bonebreak" or "Sir Frankie Crisp." He would, however, include his credentials: "John Bonebreak, M.D." or "Frankie Crisp, K.B.E."