A book on a tombstone is usually representative of the Bible, especially in rural, conservative areas. The deceased may have been a member of the clergy, or just a very religious person.
A hand pointing to the Bible indicates something deeper. This hand is pointing out the word of God, and the path to salvation it holds. A stone with this symbol on it is also showing that the deceased was a believer and is now enjoying their eternal life. It encourages observers to read and believe while they still have time.