Sticker Star serial key

In Shy Guy Jungle in Paper Mario: Sticker Star, Mario must clear a large pile of garbage to progress. However, before doing so, the player can interact with the trash to read messages left there. Among various pieces of flavor text and easter eggs is the serial key. It is unknown what, if anything, this key activates.

Theories
A popular assumption is that the serial key is for a proprietary Nintendo service. The key is not for Club Nintendo or Nintendo eShop; attempting to input it returns a "wrong code" message, as opposed to a notice that it has already been entered and used.