The following two threads provide more information on the matter of the curly quotes.
The black box to which you refer is the .notdef glyph, which is the glyph in the first column of the first row when a new font is started using Font Creator 5.0. The black box is supplied as a default design by the Font Creator 5.0 system. The design for the .notdef glyph within a font can be changed. I use various designs in fonts, though in fairness I mention that many references advise against using non-recommended designs.