The Heartagram is a symbol meaning Love Metal. It was made by the band H.I.M. or His Infernal Majesty. It is a mix of a pentagram, symbolizing metal music, and a heart, symbolizing love. This logo has nothing to do with Bam Margera, he just likes the band H.I.M. and uses their logo on his clothing and TV show.
Heart (love) + Pentagram (metal) = Heartagram (love metal)