Pentagram

A Pentagram is a five pointed star. One is used in Small Favor.

In the Series
In Small Favor, Harry Dresden is brought in a case of a burning building with its face blownoff by Murphy who smelled Hellfire in the rear of the building down the alley, suspecting magic is involved. Harry finds a sigil painted in blood and looking similar to a pentacle. Harry points out how the sigil has the five points of the star go outside the circle and that on his pentacle that he wears, the points only touch the outer circle. Harry says that it's uncomfortably like a combination of a pentacle and an anarchy symbol. — Magic unrestrained. Looking around he discovers that the sigil is only one of five reflective points with energy source coming from a different location. A beam came in from somewhere else: a whole lot of heat energy. — The beam streamed from one reflector to the next melting holes through the building. The reflectors formed the beam into one huge pentagram at ground level.something else wierd about it that ther is no trace of the magic when there should be a lot of it. Like they wiped their magic prints clean.

Description
In Small Favor, Per Harry, the Pentagram is a five-sided star. The center forms a pentagon. That is where you contain whatever it is you're trying to contain. The pentagram is a symbol of power having a lot of uses depending on how you employ it. Most often it is used to isolate or contain an entity. The bigger you make it, the more juice it takes to keep it going.

It's true north is the direction of the first line. Most often it's drawn from the bottom left to the topmost point as the first stroke. that is the way it's drawn when you want to defend something, ward something off. or banish an entity. Drawing it differently you can build a cage or open a doorway for something.

External References
Pentagram — Wikipedia

Symbolic meaning Pentacle — WikipediaPentagon — Wikipedia

Pentacle vs. Pentagram — Wiccan Information blog

Frequently Confused Symbols