You can make sigils out of essentially any letters/words, right?
Therefore, you could use the Cyrillic alphabet, or the Greek alphabet, or the whatever-alphabet-you-created, right?
Because I think this opens up a lot of really cool design possibilities when it comes to protective sigils and…
There’s belief that creating your own alphabet is the best way & to spend time developing it & working with it so it becomes second nature to use it, but if you’re not going to create your own to use one that you are most familiar with & have used the most (ie if you’re British you’d probably use the English alphabet as that’s the one you think of automatically as an adult. You’ve used it so much over your life that it has become deep rooted into your subconsciousness) & that’s exactly what you want to use when working with sigils. Your subconscious.
Basically use an alphabet you know VERY well.