Spine card

From TNL Wiki

Useless pieces of cardboard that drape the left spine of a shrinkwrapped game in Japan. They contain the UPC code and SKU and are meant to be disposed of. This is done to discourage the sale of used games in Japan. Oftentimes, the mere presence of one of these cards can increase a game's value $20+. Only the most anal and annoying F-Chans care about them, as they have no impact on the game experience whatsoever and are often not even visible (they are often placed by obsessive compulsives underneath the CD tray to keep pristine).