A pentacle's simply a talisman or amulet. Both terms "Pentacle" & "Pentagram" stem from the root word Pente, which is Greek for the number Five. No need to mystify or be condescending to those who don't know this fact. It isn't special knowledge, merely linguistics.
The inverted pentagram is simply Elements over Spirit, rather than vice-versa. The Satanist, like all Abrahamian systems usurped symbols far older than themselves. Most people believe these symbols are theirs only because they've not studied or investigated such matters further. Again...no reason to chastise someone "out of the loop"; that's for the lonely who cling onto the intangible because that lack Real station in Real Life.