I Spy

I Spy is a badge in Paper Mario. It is rewarded by Rowf in Toad Town once his Calculator is returned to him after it gets stolen by Shy Guys and taken to the Shy Guy's Toy Box. If Mario is equipped with the badge, a ringing noise plays and a Star Piece icon appears whenever he is close to a hidden panel, which can be ground pounded (after obtaining the Super Boots) to get a Star Piece. The panels can be accessed without the badge, but there is no other way to detect them. In Paper Mario: The Thousand-Year Door, the badge does't appear, but instead, Ms. Mowz is able to sniff out if any "treasure" is located in the near vicinity, which includes hidden panels.

Merluvlee's prediction

 * "I see...an I Spy Badge. I see you handing something to a merchant who cannot open his shop without the tools of his trade. You find what was stolen from him and he gives you the Badge."