There are seven features that can vary on legitimate currency, the Secret Service says. Some are expected, but others would worry most retailers.
Signature. Since the Secretary of the Treasury changes regularly, so does the signature that appears on currency.
Federal Reserve Seal. There are currently 12 Federal Reserve Banks in the United States. And all of them issue currency and stamp it with their individual seal.
Check Letter, Face Plate Number, Quadrant Number, Back Plate Number. These designations identify the specific printing plate and location of the currency.
Expected and Unexpected
Serial Numbers and “Star Notes.” Each note of the same denomination has its own serial number. If the serial number is mutilated when manufactured, it will be replaced to ensure a proper count is produced. If that happens, a star is added to the serial number to indicate it is a substitute.
Jackson’s Fingers. Andrew Jackson shows an extra digit on two years of the $20 note: 1934 and 1950. He usually has just one finger of his fist showing.
Latin To English. The Treasury Seal on $100 notes began switching to English beginning in 1966. By 1969, all $100 bills had an English language seal.
In God We Trust. The familiar motto was not added to paper currency until the 1950s. The motto was phased in between 1957 and 1966.
Source: Secret Service