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From my understanding, different symbols be it Runes or Alchemical or even astrological could be used.
Each of those things, are from a particular "system" of magic (for lack of a better term), and should not be used outside of that system. So if there is certain set of symbols that interest you, then it would be a good idea to learn more about the "system" that they come from.
Still using Runes as an example - they are not just an alphabet, they are a very powerful form of magic. Making a Sigil (as described in that thread), without knowing and understanding the Runes themselves, is frankly a bit scary.