gnus-group-icon-list

gnus-group-icon-list is a variable defined in `gnus-group.el'.
Its value is

nil

• This variable may be risky if used as a file-local variable.

Documentation:
*Controls the insertion of icons into group buffer lines.

Below is a list of `Form'/`File' pairs. When deciding how a
particular group line should be displayed, each form is evaluated.
The icon from the file field after the first true form is used. You
can change how those group lines are displayed by editing the file
field. The File will either be found in the
`gnus-group-glyph-directory' or by designating absolute name of the
file.

It is also possible to change and add form fields, but currently that
requires an understanding of Lisp expressions. Hopefully this will
change in a future release. For now, you can use the following
variables in the Lisp expression:

group: The name of the group.
unread: The number of unread articles in the group.
method: The select method used.
mailp: Whether it's a mail group or not.
level: The level of the group.
score: The score of the group.
ticked: The number of ticked articles.

You can customize this variable.