David Ovason's The Secret Symbols of the Dollar Bill: A Closer Look at the Hidden Magic and Meaning of the Money You Use Every Day is a fun book of trivia and esoterica related to our most familiar form of currency.
Many people know about the easy to spot design features of the bill, such as the 13 arrows clutched by the eagle on The Great Seal. Or, perhaps, the Star of Solomon arrangement of the constellation above the bird's head. But Ovason goes much deeper than that, bringing out geometric arrangements and deep background on the unfinished pyramid, the treasury shield, and the Omega that surrounds Washington's portrait. (And much more.)
Unfortunately, the book is arranged in an awkward style that numbers each "secret" separately. Because so many of the observations are linked, and only make sense when considered in context with others, there is a fair amount of repetition throughout the book. This makes it frustrating to read, and contributes to the feeling that some of it might be padding to make the book more substantive than it really is.
I was prepared to dismiss the book as fun, but unsubstantiated, until I reached the very end. There I discovered a series of footnotes and sources that lend credence to some of Ovason's more obscure assertions. The book would have benefited greatly by giving an indication--any indication--that these existed in the main body of the text. If you read this book, be sure to read the notes in the back as you go along, I think it will significantly enhance your enjoyment of the book.
Overall, while the book is flawed and could have benefitted from a proofread, it's a comprehensive reference that brings out aspects of the dollar's design that are not easy to find elsewhere. In the end its low price makes it a worthy addition to a library of obscure knowledge.