To be even more specific, you can target categories or even forums themselves.
For example:
.cForumRow[data-categoryid="1"]
Will only change stuff on the forum category with the ID 1.
At the same time:
.ipsDataItem[data-forumid="3"]
Will only change stuff on the forum with the ID 3.
With that in mind you can change the icon to be different for every subforum for example.