The Shake Signal is a helmet-like device that Shake wears in the episode Bus of the Undead, which lures the Mothmonsterman into his house. Shake claims that such thing "turns on whenever there is danger" (but it was on when he was watching a Dracula tv program at night). It was eventually shut down by Carl that night, which motivates the Mothmonsterman to threat the Aqua Teens to turn it on again.
In episode 26 (Super Squatter), the Shake Signal is seen at the roof of the house of the Aqua Teens. Once Shake carelessly and stupidly wires his house to Carl's in order to have electricity (since he has been shut down), one of the things that is connected is the shake signal, which is at the top of the house and starts emitting the signal which has Master Shake's shape (like the Batman signal).