Actually, it was a common signature line used in the mid-1800's. There is a doc. signed by Jeff. Davis at the Burns in Natchez -- the house where he and Varenia Howell were married -- that incorporates this. Lee and many other Gens. etc. used it as an abbreviation of a common salutation. I suspect that the convention of its use extends far further to early America and likely beyond back to Old England, too. Of course there are varients: Yr. Seldom Obt. Servant, Your Obediant Savant, etc.