Should you sign your name dr if you have a PhD?

How a PhD signs a letter depends on the recipient. If the letter is to his sister, he signs it: Love,

John

If the letter is to a friend She signs it:

Sincerely,

Joan Patrinsky

If the letter is about business or someone in a professional association, he signs it:

Very truly yours,

(Signature Sam Roberts PhD)

The Ph D follows the name.

Sam Roberts PhD Title here or in letterhead according to company policy.

Your friends will know you.