The pentagram

 

All I know about the pentagram is from horror movies and when it appears that usually means the shit's going to hit the fan. Regardless of your point of view, most people would rather gaze endlessly upon the smiley "Have a nice day!" face than see a pentagram. Some maintain that it's origins are of a benevolent nature. But, so were the swastika's. In most literature and fiction, it is used to summon demons from the Underworld or protect people from the same demons. If you're a werewolf and you see a pentagram, that means your nightlife is going to suffer some serious setbacks.