"In symbolism, an inverted figure always signifies a perverted power. The average person does not even suspect the occult properties of emblematic pentacles.
...The black magician cannot use the symbols of white magic without bringing down upon himself the forces of white magic, which would be fatal to his schemes. He must therefore distort the hierograms so that they typify the occult fact that he himself is distorting the principles for which the symbols stand. Black magic is not a fundamental art; it is the misuse of an art. Therefore it has no symbols of its own. It merely takes the emblematic figures of white magic, and by inverting and reversing them signifies that it is left-handed.
A good instance of this practice is found in the pentagram, or five-pointed star, made of five connected lines. This figure is the time-honored symbol of the magical arts, and signifies the five properties of the Great Magical Agent, the five senses of man, the five elements of nature, the five extremities of the human body. By means of the pentagram within his own soul, man not only may master and govern all creatures inferior to himself, but may demand consideration at the hands of those superior to himself.
The pentagram is used extensively in black magic, but when so used its form always differs in one of three ways: The star may be broken at one point by not permitting the converging lines to touch; it may be inverted by having one point down and two up; or it may be distorted by having the points of varying lengths. When used in black magic, the pentagram is called the "sign of the cloven hoof," or the footprint of the Devil. The star with two points upward is also called the "Goat of Mendes," because the inverted star is the same shape as a goat's head. When the upright star turns and the upper point falls to the bottom, it signifies the fall of the Morning Star."
-Manly Palmer Hall, The Secret Teachings of All Ages