The heartagram was originally created in 1996 by Ville Valo as the symbol for HIM. The band is self titled as a "love metal" band in which they use heavy metal guitar and base lines to create love songs.
The symbol looks like an upside-down five pointed star that has two rounded points of the star on top. A circle around this is common but can be left out.
The symbol is a combination of a heart and a pentagram. This pairing represents the close connection of love (the heart) and hate or fear (the pentagram), which is portrayed in HIM's music.
Although many people have seen the symbol on Bam Margera's show "Viva la Bam," the symbol is not directly related to him. Bam wears and uses the symbol on the show to promote and display his love for the band.
The symbol is not associated with the anarchy symbol, the Wiccan faith or any satanic religious groups. It is simply a logo produced by the band HIM.