They are rings that are normally yellow in color, but they turn red if missed.
Role in game
When the guitar missile goes through the rings on time, another one will appear until the target has been reached. When a ring is missed, the ring turns red and then disappears, causing the task or mission to fail or be sent back to the checkpoint (for slide levels such as "Googly-Eyes and Smelly Knick-Knacks"). They're also served on ring challenges for driving and sliding challenges.
Most of the levels they appear in are where SpongeBob performs the Sonic Wave Guitar challenges after being granted the power by Princess Mindy. To access said challenges, the player must make SpongeBob stand on a wooden floor with a starfish painted on it and then proceed to start. All of the levels where the guitar challenge is included are where Patrick is the main playable character. They also appear during the challenges of the driving and slide levels. The following is a list of levels in which they appear in.