A serial number with all of the same numbers isn’t the only kind to watch out for, you should also keep an eye out for ones with really low numbers, like 00000002, ones with really high numbers, ones with repeating number patterns like 12312312, ones that only use the same two numbers like 19919119, and flippers – ones that have a number that can be read the same even if it is upside-down, like 00069000. There are also bills that have a star instead of a letter at the end of the serial number. These bills, called star notes, replaced other bills that had a printing error. Since the Treasury can’t print a dollar bill with the same serial number more than once, they add the star.
If you want to see if your bill is worth anything because of its serial number, this fancy serial number checker can give you some idea of its value to a collector.