ido-decorations

ido-decorations is a variable defined in `ido.el'.
Its value is

("{" "}" " | " " | ..." "[" "]" " [No match]" " [Matched]" " [Not readable]" " [Too big]" " [Confirm]")

Documentation:
List of strings used by Ido to display the alternatives in the minibuffer.
There are between 11 and 13 elements in this list:
1st and 2nd elements are used as brackets around the prospect list,
3rd element is the separator between prospects (ignored if
`ido-separator' is set),
4th element is the string inserted at the end of a truncated list of prospects,
5th and 6th elements are used as brackets around the common match string which
can be completed using TAB,
7th element is the string displayed when there are no matches, and
8th element is displayed if there is a single match (and faces are not used),
9th element is displayed when the current directory is non-readable,
10th element is displayed when directory exceeds `ido-max-directory-size',
11th element is displayed to confirm creating new file or buffer.
12th and 13th elements (if present) are used as brackets around the sole
remaining completion. If absent, elements 5 and 6 are used instead.

You can customize this variable.