Such an indication could be adding a
    "(...)" to the bottom of a listing, or simply coloring hidden entries
    a darker color.

For example, the directory editor (dired) in XEmacs displays files
that end in "uninteresting" extensions (*.tmp, *.log, *~, etc.) in a
very light color. They are easy to recognize as being present but
probably uninteresting.

Of course it is all customizable. It's Emacs.

-- 
Patrick Logan                 mailto:patrickl at gemstone.com
Voice 503-533-3365            Fax   503-629-8556
Gemstone Systems, Inc         http://www.gemstone.com