I quote Wikipedia:
The pentagram is used as a Christian symbol for the five senses,
Medieval Christians believed that the "pentalpha" symbolizes the five
wounds of Christ. The pentagram was believed to protect against
The pentagram figured in a heavily symbolic Arthurian romance: it
appears on the shield of Sir Gawain in the 14th century poem Sir
Gawain and the Green Knight. As the poet explains, the five points of
the star each have five meanings: they represent the five senses, the
five fingers, the five wounds of Christ, the five joys that Mary
had of Jesus (the Annunciation, the Nativity, the Resurrection, the
Ascension, and the Assumption), and the five virtues of knighthood
which Gawain hopes to embody: noble generosity, fellowship, purity,
courtesy, and compassion.
That said, the image in question is not actually a pentagram; it's the similar five-pointed star.