D.L. Moody was the foremost evangelist and revivalist of his day and remains one of the most famous evangelists of all time. He was also the founder of Moody Bible Institute and Moody publishers. His wordless book is still used to preach the gospel in many areas of the world and his legacy continues on. His ministry continues to bear fruit today through his teaching and organizations.
Moody wrote a phenomenal explanation of Bible Marking, explaining proper marking use and philosophy and giving advice on how to mark your Bible. Perhaps even more fascinating is the look into his own marking methods. The article is so good, I wish I could post it here, but that would break copyright law, so I include the link and vigorously urge you to read D.L. Moody on Bible Marking.