The "S and double triangle" motif of Scientology's main symbol probably derives from the black magic use of the snake symbol (the "wise serpent" or Satan) combined with a deconstruction into two triangles of the Star of David (rather like the reverse ritual of hanging the Christian cross upside down to signify devil worship). This symbol - the magical hexagram - was used by Hubbard and Parsons during their attempts at incarnating the Antichrist in human form.
The RTC (a main Scientology corporation) symbol contains the Dianetics triangle, which is a common magical symbol, representing the door of the Cabala, the letter Daleth. Hubbard indeed assigned it to the Greek equivalent of Daleth, Delta. The triangle on its base is also the symbol of Set, the Egyptian god called by some "the destroyer of man", the male equivalent of Babalon. Indeed Crowley equates Set with Satan. Hubbard also used the "Daleth" triangle of the Egyptian destroyer-god Set as the Dianetic symbol.
Hubbard copied the back of Crowley's Tarot-cards, a distinctively marked cross, which he used for his main Scientology church cross and symbol.
The Sea Organization symbol of Scientology's elite paramilitary division is also interesting. The five pointed star, or pentacle is the most commonly known symbol of magical power. It is held between two thirteen-leaved laurels.
The theta symbol used by Scientology is the central symbol of Crowley's Ordo Templi Orientis, where it denotes "Thelma" or the will. Perhaps Hubbard's "thetan" is pronounced to match with a lisped "Satan"? He was, after all, wry in his humor and such a subtle perverse twist and deceit of lower initiates would be entirely congruent with classical Satanism.
Crowley's order - the OTO - had a common origin with the Thule group to which several members of the Nazi hierarchy belonged (including deputy party chairman Rudolph Hess). The sig rune used by the Nazis - appears on the Scientology International Management Organization's symbol - a red square enclosing a white disc and set off by four lightning flashes or sig runes. The swastika of the Nazi flag has been replaced by the Scientology "S and double triangle". The symbol of the Religious Technology Center is surrounded by sig runes. The sig rune is otherwise peculiar to the Nazis.
L. Ron, junior, was sure that the teachings of the pre-Nazi Germanen Orden and the Thule secret societies had passed directly to his father by courier. No explanation is given for using these sig runes by Scientology. At the time that both of these symbols were introduced, Hubbard also created the International Finance Police, headed by the International Finance Dictator. An significant choice of words.