When the writing of handwritten physical letters was popular, it was not uncommon to end a letter with a valediction similar to “Your humble servant,” etc. More recently, people often ended letters with “Yours truly,” or “Sincerely yours.” But according to this article, both of those are actually abbreviations. It explains:
While one may think that the word “Yours” is a type of possessive form, it doesn’t mean that at all. It actually is an abbreviation of “Your Servant” — typically written: yours and abbreviated today as “yours”. So both “Sincerely Yours” and “Yours Truly” actually mean “Sincerely your servant” and “Your servant truly”, respectively.