"" This U.S. $1 bill has been marked as a replacement note. Notice the star located at the end of the serial number. BANKNOTEWORLD/HOWSTUFFWORKS All modern United States currency contains either a 10- or 11-digit serial number in order to make each bill unique. Ten-digit serial numbers were on all bills until the "new style" came out in 1996. Those bills (and all produced since then) have an 11-digit serial. The serial number consists of the following: The first letter, only found on the new-style bills, represents the series of the bill. The series indicates the year in which the design of the bill was approved for production. This begins with A, and moves through the alphabet each time a new series is needed (for example, each time there is a new secretary of the treasury, the bill design changes because the secretary's signature is on all currency). You can also find the series of the bill printed directly to the bottom-right of the portrait.The second letter (or … [Read more...] about Why Do Some U.S. Bills Have a Star at the End of the Serial Number?