The conch signal is light purple and resembles a regular conch shell, except it is much bigger.
Role in episode
After winning a contest, SpongeBob wins the conch signal and uses it to see if it works. This causes Mermaid Man and Barnacle Boy to hear it and come to SpongeBob's house. They warn SpongeBob that it is not a toy and should only be used in emergencies.
SpongeBob uses it to call them so that they can help him open a jar of mayonnaise. Barnacle Boy is angry that SpongeBob has used it in a false alarm. Mermaid Man convinces Barnacle Boy to let SpongeBob use the conch for minor favors because superhero emergencies do not come up very often.
SpongeBob uses the conch signal several more times until the super duo is tired. Barnacle Boy takes it away from SpongeBob and tries to burn it with his heat vision, but is unable to because of his age. He then puts it in his pants and says that he will destroy it later.