The inverted Pentagram (in most cases) is a negative/evil symbol that represents the implication that the spirit is subservient to matter, and that man is subservient to his carnal desires.

For this reason it was used on the ‘Devil’ Tarot Card, and also was used by Satanist Anton Lavey as the symbol for the ‘Church of Satan’.

“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 P. Hall – The Secret Teachings of all Ages

"The Pentagram, which in Gnostic schools is called the Blazing Star, is the sign of intellectual omnipotence and autocracy. It is the Star of the Magi; it is the sign of the Word made flesh; and, according to the direction of its points, this absolute magical symbol represents order or confusion, the Divine Lamb of Ormuz and St. John (upright), or the accursed goat of Mendes (inverted).”

– Eliphas Levi

“A reversed pentagram, with two points projecting upwards, is a symbol of evil and attracts sinister forces because it overturns the proper order of things and demonstrates the triumph of matter over spirit. It is the goat of lust attacking the heavens with its horns, a sign execrated by initiates.”

– Eliphas Levi – Transcendental Magic, its Doctrine and Ritual

“The flaming star, which, when turned upside down, is the hierolgyphic sign of the goat of Black Magic, whose head may be drawn in the star, the two horns at the top, the ears to the right and left, the beard at the bottom. It is the sign of antagonism and fatality. It is the goat of lust attacking the heavens with its horns.”

– Eliphas Levi – The Key of the Mysteries

“Let us keep the figure of the Five-pointed Star always upright, with the topmost triangle pointing to heaven, for it is the seat of wisdom, and if the figure is reversed, perversion and evil will be the result.”

– Franz Hartmann