This book is a Harper and Brother's Author's National Edition. They were produced from 1909 - 1916. This book was volume 2 of a set of 25 volumes.
The binding is red cloth which was stamped to resemble leather and featuring gold lettering. This was one of two optional types when ordering the collection.
Your book was an early version, made prior to 1913. In 1913, Harper and Brothers changed the binding to feature a cameo of Samuel Clemens on the cover.
Each volume includes the signature, "This is the authorized Uniform Edition of all my books. Mark Twain." That is a printed signature with no value.
When the series was for sale in 1909, you could buy the entire collection for $25. Today, you can still find the entire collection available for around $150 - $200.
Keep in mind that during World War 1, there were over 1 million copies of this collection sold.