The Big Book of Reiki Symbols
The Spiritual Transition of Symbols and Mantras of the Usui System of Natural Healing
by Mark Hosak & Walter Luebeck

There are many books now available on Reiki, but this one is unique. It provides a detailed and profound explanation of the traditional Reiki symbols and mantras, with their spiritual traditions, their calligraphically correct spelling, their meanings and functions. The book is a standard guide on Reiki based on years of research and supported by experiences with thousands of students and individual sessions, offering the reader - whether Reiki Masters or practitioners - a careful and well-organized presentation of the material with expert correctness. 

This is a big fat book: 665 pages