These days, a pentacle or pentagram has many meanings and connotations. People often think that the pentacle is an evil sign. Many Christians, and indeed much of the Western world, associate it with Satanism and witchcraft. While it's true that Satanists do use the pentacle in their rituals, it is certainly not a Satanistic sign, nor was it first used by Satanists. Unfortunately, few are able to differentiate between Wicca and Satanism.
It was the Sumerians who first utilized the pentacle symbol. For them, however, it was merely a piece of their language rather than a religious symbol.
As you read earlier, Satanists do indeed use it as a symbol, typically with two points up and three down. They refer to this as the Sigil of Baphomet, and it is used as a symbol for Leviathan.
It was also the official seal of Jerusalem for a while, showing its presence in Judaism as well in Christianity, it was used to represent the five senses. In medieval times, it was believed to represent the five wounds of Christ (two in the wrists, two in the ankles and one in the side). At this point, its common use was actually to ward off demons and witches, which becomes ironic later on.
It has also represented the five fingers, the five joys Mary had of Jesus, as well as the five virtues of knighthood. However, it later became thought of as an evil symbol. Pagans and Wiccans use the pentacle in their rituals, as do Satanists, albeit in completely different manners. This led Christians to believe the pentagram to be an unholy symbol of evil, something that's carried forward to today.
Lastly, we come to Wicca and Neopaganism. The pentacle is a very important symbol in these religions. Many versions of the religion use it as their holy symbol, and wear it as Wiccan Jewelry, much like Christians have the Cross of Jesus and Jews have the Star of David. While not quite as universal as these other symbols (some branches of Neopaganism rarely, if ever, incorporate pentacles into their rituals), witchcraft is one of its main associations.
As previously mentioned, few are able to shake the thought that witches are evil, and pentacles add to this. However, Wicca and Neopaganism in general are vastly different from Satanism.