Those aren't "Apple's glyphs", they're part of the ISO/IEC 9995 standard for common keyboard layouts. https://en.wikipedia.org/wiki/ISO/IEC_9995 Perhaps Emacs and the Linux desktop should start using these characters by default, seeing as they now have good Unicode support.
I find it harder to scan my eyes over Ctrl+Alt+a than C-M-a (notice that Apple, too, uses single glyphs for modifier keys).