I’m very interested in railroad signaling so I bought the book Railroad Signaling by Brian Solomon (MBI Publishing). For anyone, this will be a great source of information to learn the history of signaling, how it evolved, and how it is used today. Because of the explanation of the evolution, this book is useful for anyone interested in any period of railroading.
The author also refers to many additional resources, so if you are like me and really want to know signaling inside and out you have places to go for more info. I am a very logical person, a computer programmer by training and heart, and learning how the various signals interact with each other is like a nice, complex logic puzzle I wish to solve.