I used "|x|" notation because I don't like introducing new unknown names if I don't have to. Too bad the annotation is ambiguous; I'll make a note about it.
If you right-click on the math blocks, you can change some of the parameters of the MathJAX renderer. One feature I've found helpful is the "click to zoom" which can be activated by following `Math Settings -> Zoom Trigger -> Click`.
I tried changing the text color. How does it look to you now?
Math notation is not great generally. There are canonical notations for somethings, and some times they're overloaded. Not much to do about it other than know about it.
Annoyingly you have to "know your audience" to get your math notation right for who you're presenting to. (You can never really do that on the Internet)
As an electrical engineer who's done a lot of DSP and worked with mathematicians I can point out some things that look either odd or normal depending on who I'm talking to. You can never really win with notation -- you'll always be wrong to someone =), but there are choices that are maybe less wrong for one discipline or another.
All that to say keep writing! You're doing pretty well!