The pentacle has long been associated with paganism and most earth-based religions. Yet it seems the influence of the media and Hollywood has made it come to represent anything evil or Satanic in nature. However nothing could be further from the truth. The pentacle is the ultimate symbol of good and protection.
The five points of the pentacle represent the elements: spirit, water, earth, fire and air. The circle around the star represents the protection and presence of these elements within a living creature. In addition it represents the connection and unity between the elements. It is one of the most powerful protection symbols in paganism. When worn rightside up it represents the Goddess and the spirits of human being. When used inverted it represents the God and higher spirituality. To my mind there is nothing negative there.
Christianity is largely responsible for the misconceptions surrounding the pentacle. It was originally Christianity's goal to "baptize" the pentacle and turn it into a Christian symbol. As it is much easier to convert people to your faith if they are familiar with the symbolism, Christianity adopted the pentacle thusly. Christian faiths used the pentacle to represent the 5 wounds of Jesus Christ in an effort to better convert local pagans. When this effort was complete, the pentacle was then demonized by Christianity as a demonic or evil symbol.
The pentacle is also commonly associated with Satanism, which is in no way a representation of common practice. It is true that satanists use the inverted pentacle as a symbol of power, but it in no way represents anything negative or evil even in that context. Pagan symbology is not generall used in Satanism because Satanism is essentially an inversion of everything Christian. As the pentacle is not typically Christian, it is not used much in Satanism. It is much more likely that you will run into an inverted cross being used at a Satanic ritual than a pentacle.
All in all, the pentacle is one of the oldest symbols of goodness and protection that exist today. It has been used for thousands of years and has been used by hundreds of earth-based religions. It is a popcular misconception that the pentacle is a sign that one is in league with the devil or have otherwise evil intentions. Which, in my opinion, is a shame as there are few symbols in any faith that can inspire such light and positivity.