I assume you mean the star made with a single unbroken line which crosses itself, as in a pentacle? In Catholicism, a pentagram either hollow or filled, but not with the lines, is an iconic reference to Mary, mother of Jesus. The Pennsylvania Dutch -- Amish or Mennonites of German origin -- use the pentagram in their art, not just in the so-called "hex" signs but also in woodworking, such as furniture items and decorative rails (like the rail around a porch). It is a religious motif for them, but I don't know what its particular meaning is. Two nation's flags use pentagrams now, and neither appears to be associated with Christianity. Morocco adopted a green pentagram on their red flag in 1915: http://www.tiscali.co.uk/reference/encyclopaedia/countryfacts/morocco_flag.html but they refer to it as "Solomon's Seal" and it may also be a remainder of the conflation of Ishtar with Fatima, daughter of the Prophet Mohammed, per this site: http://www.crwflags.com/fotw/flags/ma.html And when Catholic Spain occupied parts of Morocco, they continued to use the pentagram, swapping it out for a six-pointed star for some uses: http://www.crwflags.com/fotw/flags/ma_es.html And the French Protectorate of Morocco used the same pentagram flag: http://www.crwflags.com/fotw/flags/ma_fr.html Though the French & Spanish occupiers were Christian, that doesn't appear to be why the pentagram was used. Ethiopia's flags have had Christian symbols in the past (St. George and the dragon, e.g.), but the blue emblem they adopted in 1996 for the center of their flag, a pentagram with rays between the points, is not Christian, but "a radiant star with equidistant rays to show the equality of all ethnic groups as well as creed and gender equity. The shining rays from the star testify to a bright future for Ethiopia, and surrounding the emblem will be a blue background to denote peace and democracy in Ethiopia." http://www.crwflags.com/fotw/flags/et.html

I have seen them in sigils that are related to the names of the arch-angels. I have this big book of signs and symbols that had them in there.

They were also used centuries ago to represent the 5 wounds of Christ.

According to Heather Child's Christian Symbols, Ancient and Modern[6], the pentagram is a symbol of the five senses. Also, when the letters S, A, L, V, and S are inscribed in the points, the pentagram is a symbol of health (Latin salūs). Medieval Christians believed it to symbolise the five wounds of Christ. The pentagram was believed to protect against witches and demons.[7] The pentagram figured in the heavily symbolic Arthurian romances.[7] It appears on the shield of Sir Gawain in the 14th Century poem, Sir Gawain and the Green Knight. In the poem the five lines of the star are given multiple meanings: they represent the five senses, five fingers, the five wounds of Christ[8], 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: frankness, fellowship, purity, courtesy and compassion. Probably due to misinterpretation of symbols used by ceremonial magicians, it later became associated with Satanism and subsequently rejected by most of Christianity sometime in the twentieth century.[7] The Church of Jesus Christ of Latter-day Saints has traditionally used pentagrams and five-pointed stars in Temple architecture, particularly the Nauvoo Illinois Temple[9] and the Salt Lake Temple. These symbols derived from traditional morning star pentagrams that are no longer commonly used in mainstream Christianity wikipedia

the seal of King Solomon, or Solomons sigil