I like the simplicity of the moon symbol, however it's similarity to the crescent and star might be confusing for some and offensive to others.
Yes, now I begin to think that could be an issue.
Also maybe looks "wiccan".
Thinking to set this idea aside for now.
Honestly, I'd be more inclined to adopt the 20er moon given those others who use moons. Nobody has a monopoly on the phases of the moon.
PS. In light of that, I've taken Kalosyni 's version of Eikadistes' 20er moon phase and added 4 atoms of 4 different sizes in a diamond pattern inspired by Godfrey 's post above. I'm saying they represent atoms (varying in size) as well as the 4 lines of the Tetrapharmakos. I could have gone with three for the Canon. To be clear: I'm NOT endorsing this. Merely playing and "trying it on for size" for a little while.