Agree, though to add context for the developer, even before formal Wicca and the Hermetic Order of the Golden Dawn, the pentacle's been around for ages. Older traditions, despite the name seeming to imply five points (the name most likely derives from "pend" meaning "to hang", rather than "pent" meaning "five"--so like the word "pendant", which is essentially how pentacles were and still are worn by some practitioners), also had pentacles with 6 or 7 pointed stars, perhaps most notably in the Key of Solomon. All this to say, essentially, that despite the long history, uses in different traditions, and the varying appearances, pentacles have universally been used for protection.
Personally, my suggestion would be to create a sigil or pentacle of your own design (ala the famous Necronomicon pentacle), or perhaps weave the protective use of the pentacle into the lore (for example, the author placed the symbol on the cover of the book in an attempt to protect the author or reader from the evils within... but this failed).