If you haven't heard, there are tens of thousands of dollar bills out there that are worth way more than face value. While sometimes it is because of some kind of error, more often than not, the value skyrockets because of the bill's serial number. You'll always want to keep an eye out for bills with really low numbers, like 00000001, ones with really high numbers, ones with repeating number patterns like 12341234, ones that only use the same two numbers like 12212122, the rare ones with the same number, and flippers - ones that have a number that can be read the same even if it is upside-down, like 00069000. But there is another thing to be on the hunt for - birthday notes.
A birthday note is one that has a serial number that is a specific date, like 08151980. Anyone born August 15th, 1980 would love to have that as a souvenir, so much so that they'd be willing to pay a lot more than $1 for it. Recent birthday notes have sold on eBay for $30.
If you want to see if a bill you have is worth anything because of its serial number, this fancy serial number checker can give you some idea of its value to a collector. As for what to do if you have a bill that's unique - you can try a pawn shop, eBay or find a collector's group on Facebook and list it there.