Update : I apologize to A. Lewis for my error.
I’ve found that this website : http://www.awpcp.com/premium-modules/category-icons-module/ is selling a WordPress plugin called Category Icons for $10.99 !!! Here is how they describe it :
Category Icons Module
Category Icons Premium Module for Another WordPress Classifieds Plugin – $10.99
This module allows you to add icons to your categories and subcategories. The silk icon pack from famfamfam.com is included in the default package. You can always use your own icons by uploading them to the images/caticons folder. Adding your icons is a simple matter of selecting the icon you want to use for a specific category and clicking a button to set it. (If you have previously made a donation of $10 or more please contact me for a free copy of this module)