Many Charmed fans ask "What is this Symbol ?".
This is an ancient symbol called a triquetra (pronounced tri-KET-ra) which is latin for three-cornered.
What about its history ? Where did it come from ? Nobody knows for sure, but a three-cornered symbol has appeared in many cultures throughout the world, the earliest example being from 5000 year old Indian artifacts. This particular symbol was and still is used by the Christian faith (take a closer look at your local church and you will probably find at least one example). Now whether the christians "acquired" this particular symbol from the pagans who were also using this symbol no one knows, although it is known that christians acquired various symbols and religious holidays (Christmas is one example, it was originally a pagan festival that celebrated the winter solstice)
What does it signify ? The number 3 is important to many cultures and in nature, so it's not surprising that a symbol of this type appeared. I will only concentrate here on it's meaning for two cultures. If anyone knows of any other meanings let me know and I'll publish them here.
Pagan/Wiccan/Goddess Symbolism It symbolizes life, death, and rebirth and the three forces of nature: earth, air, and water. The inner three circles represent the female element and fertility. It is also known as the Triple Goddess. the Maiden, Mother, and Crone represent the life stages of every woman (and man). born to innocence, inspired to create, then embodied with wisdom. The triquetra is a symbol of protection. It represents the safety of a witch while she is wearing it or showing respect for the wiccan religion.
Christian Symbolism The Triquetra represents the Holy Trinity: the Father, Son, and Holy Spirit. The unbroken circle represents eternity. The interwoven nature of the symbol denotes the indivisibility and equality of the Holy Trinity. It symbolizes that the Holy Spirit is three beings of power, honor, and glory but is indivisibly one God.