Additionally, within the scope of any one field or sub-field, you get a nice constant-factor boost by exploiting capital/lowercase, italics, bold-face, "chalkboard" font, etc. and usually that suffices. Anyone who has taken a linear algebra course instantly recognizes what I mean by "Solve Ax = b" in the appropriate context. And if I say "Solve Qx = b" you have even more information, etc.

Yes single letters but using greek, latin, fracture, small and capital. Only small fracture is rare though.