I just hit Google with Pentagram as it occured to me that it couldn't
just be something to do with horsehair shirt wearing yogurt weavers trying to conjure up non existant gods (as if there were any gods that do exist, that is) and what I found was fairly interesting.
HERE.
Seems that its been associated with Venus and I never knew that was it's self regarded as lucifer (bringer of light) but when you consider when Venus is often seen it makes sense. Anyway the christians nicked it as a symbol for a bit and have also vilified it as being evil which is no surprise as they have a habit of calling all other false gods evil.
Notice that I make no distinction between supposed true gods and supposed evil false gods cos till I see any concrete evidence of any of them I will continue to regard the lot of them as meaningless mumbo jumbo.
What I am trying to say is, if your the kind of person that gives a flying **** about christianities little insecurites a pentangle may hold some power if not its just an interesting shape