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An Outsider shared the Glyphs with us.
The Glyphs that are known to be usable with the ritual are included and their meanings are their titles. They are elemental. You could try to adapt the ritual to use sigils of your own devising.
If however you want to try and create a new Glyph, as far as I've been able to discern they are made up of 4 straight lines, 2 circles, and a curved line.
Symbols that do not conform to this pattern are present in the document, but they are from a different language set that I was not able to translate and were included as decoration. I suspect that may have been their original purpose or they could be logos, names, or transcription errors.