org-columns-ellipses

org-columns-ellipses is a variable defined in `org.el'.
Its value is

".."

Documentation:
The ellipses to be used when a field in column view is truncated.
When this is the empty string, as many characters as possible are shown,
but then there will be no visual indication that the field has been truncated.
When this is a string of length N, the last N characters of a truncated
field are replaced by this string. If the column is narrower than the
ellipses string, only part of the ellipses string will be shown.

You can customize this variable.