The symbol on the Book Of Shadows - The symbol is called a Triquetra, which is supposed to represent the Power of Three, which Phoebe suggests. Later Prue suggests it represents the three of them working as one. The Triquetra is also a feminine symbol of protection from evil, that were form by three yonic vesicas. Triquetras can appear with the symbol or with out. The three vesicas represent the triple Goddess and when the circle circle, when used, represents eternity.