Hank states that the inverted triangle symbol was used by the Order of The Golden Dawn in Wiccan practices in the 18th century. However neither the Order or Wicca existed in the 18th century. The Hermetic Order of The Golden Dawn was founded as a secret magic society in the late 19th century, whilst Wicca was founded by Gerald Gardner in the 1950s.
Crucifixion is a horrific method of murder, just tying someone to a wooden cross would make them a scarecrow. And since that isn't fatal, none of the victims were crucified. (Just like trying someone to a guillotine and shooting them wouldn't mean they were guillotined.)
It's also no part of Satanism, crucifixion is almost exclusively a Roman form of execution. Satanists can't even invert it like they do with the Christian cross or the pagan pentagram because crucifying people upsidedown was already used; on St. Peter, one of the Disciples.
The triskele has never had anything to do with druids. It is an ancient Celtic symbol which represents the balance of 3 elements joining to make a whole: earth, air, and water; mind, body and spirit; birth, life, and death; the maiden, the mother, and the crone.
It is in fact the earliest know religious symbol, dating back to between 5000-3000BC and (along with the triple moon) is the symbol of the Goddess The Morrigan, also known as the Triple Goddess.
The Morrigan is the maiden, the mother, and the crone, she is also the goddess of birth, fate, and death.
The triskele (from the Greek "triskeles" meaning "three legs") has never had anything to do with water, except that water makes up a lot of the world. Earth, sky and water are just what the world is made of, there's no hidden meaning.