It's worth very little, unfortunately. The date of the printing far exceeds the date of a First Edition and, more importantly to your question, books containing an illustration of Mark Twain with his signature underneath are mass produced printings, and are not actually signed by Mark Twain (Samuel Clemens). I happen to have a bonafide first edition of this work, but its endorsed title page is steel engraved as well... very few of Clemen's works were provably autographed. Those that do exist are usually sets of his works and contain both the Mark Twain and Samuel Clemens autographs as well as additional information... Enjoy your old book though and hand it down as a memento of an age gone by...