The signature is thought to be one of the oldest ever autographs penned by the King, who died at the age of 42 in 1977.
Source:
http://www.historyofelvis.com/elvis-news/elvis-presley-a-read-fit-for-a-king-forgotten-library-book-and-card-signed-by-the-king-of-pop-go-under-the-hammer/