If used for religious identification, it would be of a satanist, not a wiccan symbol. And yes, the three points at the bottom represent rejection of the holy trinity and the two top points are "thrust upward in defiance" of herd conformity, blind dogmatic living, etc. A cliche sentiment of alternative culture for sure, but it is often reflected in his lyrics and answers to interview questions.
I didn't know that he used it upside down, I've never had the pleasure of meeting him or getting him to sign something. V.V
I am not sure why he does it, but I'll tell you this. It sure causes me to get some dirty looks in the Baptist school carpool line when I roll through wearing the shirt he signed on the right sleeve and they are loading my 5 year old into the passenger side. ha.