He was a member of the O.T.O, or Ordo Templi Orientis. The order’s famous motto is “Do what thou wilt shall be the whole of the Law”, which corresponds to the number 93 in gematria. The number is used as a greeting among initiates 😎 That explains the obscure reference. Jack Parsons was a devoted Thelemite
Discussion
I didn't know the 93 part! But now it makes sense why I see that on all their literature!