The Cat Bell (鈴, Suzu) is an item used as proof of being sent to see Kami at Kami's Lookout.
Goku receives the Cat Bell from Korin on Korin Tower and shows it to Mr. Popo, to prove that he is qualified to challenge Mr. Popo for a chance to see Kami. It first appears in the chapter The Nyoi-bo's Secret and the episode "Temple Above the Clouds".
A similar bell is seen on Mr. Popo's cat. While Goku needed to learn about seeing without seeing, Mr. Popo blindfolds him and asks Goku to catch the cat, which had the bell tied to its tail.
The bell also appears in the video game Dragon Ball 3: Gokuden.