Ninety-three (93) is one of a series of symbolic numbers that is associated with Aleister Crowley's theosophical system, Thelema. It is commonly seen in the salutations and closes of letters written by members of the OTO (Ordo Templi Orientis) or by other Crowleyan followers.
Love Under Will
Crowley chose this number as a summation of his philosophy because, according to gematria (or rather 'isopsephy,' as it is Greek), this is the value of both Greek Thelema (Θελημα), meaning Will, and Agape (Αγαπη), Love. According to the general principle of gematria this means that the two are complementary and/or related concepts. The most well-known and most thoroughly misunderstood of all Crowley's utterances is that which defines his entire doctrine: "Do what thou wilt shall be the whole of the law; love is the law, love under will."
Most letters of the OTO begin with the first half, i.e. "Do what thou wilt shall be the whole of the law," and finish with the second - "Love is the law, love under will." 93 is simply a shorthand way of writing this.