Sigils are the pictorial or symbolic representations of elements in magical practices. Historically Sigils have been used to represent other world entities such as Demons, Angels, Djinn and Spirits with each entity having there unique symbol (Sigil). These Sigils have been used to either summon or control (as in King Solomon’s times) these beings for purposes of magick.
Some old Sigils were created by using the ‘knowledge of numbers’ (which is an ancient knowledge only a few know now) here the name of a Demon, Angel or Spirit were converted into numerical values (maths is a more basic and universal language), these numbers were then used in the creation of those Sigils.
Modern Chaos magic practitioners have adopted a technique first devised by Austin Osman Spare to create new Sigils which represent thought forms and actions the Magician wants to put into affect in the real world. In this technique the wizard first focuses on a thought, he then puts that into words, in the next stage he takes out all the vowels and repeating alphabets in the sentence and forms a single word. He now uses his creativity and imagination to arrange those alphabets into a symbol, he has now created new Sigil.
This modern technique though may be useful to some extent it is not as powerful, firstly because the language mostly used is simple English and then it is further altered to form the Sigil. That is why it is recommended to use ancient Sigils which were formed by more basic forms of language and maths, as this is nearer to the origin and hence more powerful.
It is my belief that even more powerful Sigils can be created using even more basic elements. For example when you here music a story starts to form in your mind, even though no are words said, hence a musician can form thoughts and stories by sounds alone. A master magician can then form true symbols (Sigils) by thoughts alone, this the essence of powerful Sigil Magick. It is possible some powerful sigils like those used by King Solomon to enslave demons and djinn were created by these means and it is possible there are yet even more powerful Sigils left to be discovered.