According to Éliphas Lévi, this forms part of the inscription on a pentacle that was a frontispiece to the published Grimoire of Honorius, an antipope of the thirteenth century. The letters, used to designate a name of God, were reversed on the pentacle, said to be part of a ritual for the evocation of evil spirits.
"AL" was also a word of considerable importance to magician Aleister Crowley. It was the name given to the revelation he received in 1904 that became the basis of his new system of thelemic magic, usually called The Book of the Law or Liber AL. Crowley placed great store in numerology. In his system, AL equated to 31, the number which he felt held the key to unlocking the meaning of Liber AL.
Lévi, Éliphas. The History of Magic. 1913. Reprint, New York: Samuel Weiser, 1969.