In the church of Satan, this pentagram is called the Anton LaVey sigil, because for a while he was using it as a personal symbol. It was also used for a time to denote rank within the church, although this is no longer being used. The bolt represents the flash of inspiration that drives people to greatness and which is necessary in Church leadership. The lightning bolt is based on the lightning bolt used in the logo for RKO Radio Pictures. That connection has no inherent meaning in it beyond LaVey's aesthetic appreciation for the graphic. It is not, as some have suggested, a Germanic sig rune, which the Nazis adopted for their SS logo. Some theistic Satanists also use the lightning bolt pentagram. It represents power and life-force descending from Satan into matter.
Excerpt taken from www.about.com - Catherine Beyer/About.com