What does a 'glyph' represent?

Hi all,

I was randomly playing with menus in RH11 when I selected View > Show > Glyphs. Obligingly, a glyph showed up in the open topic. Except I don't know what it represents. "No worries," says I, "I'll check the help". Which helpfully tells me how to turn them on and shows me what they look like, but which doesn't tell me what exactly they are.

Adobe RoboHelp 11 * View topics and design elements

Does anyone have any insight into these funny red squares?