Reply To: Adding a glyph to a numbered list…

Cool idea to use brackets.
Another idea might be to use a custom font that has both numbers and a square box.

Or (this is crazy, but it works) you could fake a square by applying a rule above and a rule below to the paragraph, and set the positioning and thickness of the rules so that one “knocks out” the other, except for an outline of a square in the proper location.