What was so revolutionary about chaos sigil magic was not only its orientation towards practical real-life results but also the idea that you can create personal sigils yourself without having to rely on the traditional ones in ancient grimoires anymore. It gave magicians back their autonomy who now didn't have to follow strict formulae and recipes any longer and were encouraged to experiment instead. In fact, when you read the instructions in Liber Null & Psychonaut by Carroll or Practical Sigil Magic by Frater U.D., you'd be forgiven to suspect that the Sentence of Desire formulation => sigil creation process was some sort of Waldorf schoolchildren's game. A chaos sigil is what you want it to be and means what you want it to mean, and no one has the right to tell you otherwise. It's your personal creation, your baby.
Practicalities: my view is that a chaos magic sigil has to be impressive (= to yourself of course); I don't think much of sloppily drawn sigils. Some care should go into their creation, and you may have to discard several drafts until you end up with one you're satisfied with. Personally, I don't throw out the vowels because I like to reinforce the sigil with mantras constructed from the letters, and you'll need vowels for that. A sigil should be complex enough to disguise the underlying letters so that you won't be able to guess its meaning easily but the level of distortion, abstraction, etc. is solely up to you. You can even add symbols that have personal significance for you (I myself like using exclamation marks to denote urgency). Sometimes simplicity or symmetry is a good idea though, for example when you want to visualise your sigil while reciting the associated mantra.
Experimentation, however, means that you'll have to develop your own procedures without recourse to self-appointed 'authorities'. Some technical aspects of Carroll's original methods have come under question, e.g. his insistence that any thought of a sigil's purpose must be avoided at all costs - I think it's ok to remember one's desire but not the magical operation you performed to achieve it. Similarly, I somehow doubt the concept of the Psychic Censor but haven't made up my mind yet in this respect. But that's the idea of chaos magic, you make up your own rules and later maybe abandon some of them if they don't prove to be useful. Nevertheless, prepare for some rather sketchy results in the beginning, freedom to experiment also includes the freedom to fail.
