Collection serial numbers that have 0, 6, 9


Paper money has 0, 6 and 9 which if in a note the 0 number appear the same right side up or upside down, the 6 and the 9 would read either 6 or 9 dependant on the being upside down or not.

There are collecters whom collect notes that have only those numbers, what is the name for this type of collecting and is there a vary large following?

These notes are known as flippers. Whether there is a huge following for this type I don't know, it appears to be a newer type of fancy serial number collecting.

http://oldcurrencyvalues.com/Flipper_Serial_Number.html