This hand is a key element in the film's overall aesthetic of camp, horror, and sexuality. It's a prominent symbol of the film's playful, even macabre, sense of humor.
While the exact meaning of the hand is open to interpretation, it can be seen as representing the dominance and power of Dr. Frank-N-Furter, the film's villainous protagonist.
The mural also serves as a striking visual element, creating a surreal and unnerving atmosphere in the pool scene.