If you are sending a letter acknowledging a compliment or some kindness done you may say, Yours gratefully, or Yours very gratefully, in proportion to the act of kindness received.
It is not customary to sign letters of degrees or titles after your name, except you are a lord, earl or duke and only known by the title, but as we have no such titles in America it is unnecessary to bring this matter into consideration. Don't sign yourself,
Sincerely yours,
Obadiah Jackson, M.A. or L.L. D.
If you're an M. A. or an L.L. D. people generally know it without your sounding your own trumpet. Many people, and especially clergymen, are fond of flaunting after their names degrees they have received honoris causa, that is, degrees as a mark of honor, without examination. Such degrees should be kept in the background. Many a deadhead has these degrees which he could never have earned by brain work.
Married women whose husbands are alive may sign the husband's name with the prefix Mrs: thus,
Yours sincerely,
Mrs. William Southey.
but when the husband is dead the signature should be—
Yours sincerely,
Mrs. Sarah Southey.
So when we receive a letter from a woman we are enabled to tell whether she has a husband living or is a widow. A woman separated from her husband but not a divorcee should not sign his name.