There is a lesser known Snap to Glyph command in context menu, which allow you to snap to any live glyph under cursor. It requires Smart Guides and Snap tp Glyph commands enabled (and Snap to Grid disabled).

Once you enter the mode, the chosen glyph is highlighted with a rectangle, and you are able to construct new art relative to points of this live glyph, as if it was outlined.
These guides are green, similar to normal Glyph Guides, but some guides are unique to this mode, like the 'angular' one — which allows us to build on a continuation of an existing straight line — similar to what 'Line Extension' smart guide does (when not broken).

This guide is missing in a non-glyph world, and it’s rather cool, and we’d benefit from having it for everything else, for all other tools: Pen, Selection, Scale... Please make it happen and add it as a n option in Preferences > Smart Guides.