The series year is also printed separately on the currency, in between the portrait of the historical figure (such as Lincoln on the $5 bill) and the Secretary of the Treasury’s signature in the bottom right part of the bill. The years are represented by letters A-P as follows: On bills worth $5 and up, each serial number begins with a letter, which tells us the series year of the bill. They are accompanied by other identifying letters and numbers that tell us which series year the bill is from and where it was printed. Serial numbers are eight-digit-long codes that are unique to each bill. This graphic shows how to read the numbers on paper money.
