Most discs are stamped on the top but this collection of discs are stamped on the bottom. Some players prefer the clean look of a disc, others buy these so they can dye them and customize them at home. These discs come in putter, midrange, and driver options. Compare the price of a top stamp and a bottom stamp and they're the same, it's just a way to customize your bag and doesn't affect the flight of the disc.
Players who have a tour series disc with a bottom stamp tend to have a featured stamp on top as well. There are plenty of options for molds and plastics that a bottom stamp is available in. Check out all these discs and find one you like!