Threaded view - shows squares

["David Fishburn" <fishburn@xxxxxxxxxxxxx>]

Mutt 1.4.1i (Cygwin)

When I open my mail file using the threaded view, I see this:
[]=>
[][]>
   []=>
   [] []>

So it looks like it is trying to display a character my machine does not
support.
Is this configurable (like everything else in mutt)?

Thanks,
Dave