The three class combo statuses (Brittle, Staggered and Disoriented) each have an icon that is given whenever they are mentioned on the ability description pages. Whenever a combatant is suffering from one of these statuses, they have a three-dimensional version of the icon floating above them.
The easiest way to take advantage of the class combo statuses is to configure your party members' tactics so that they respond to an enemy who has the relevant status with a relevant ability.
I couldn't find any images of the icons for the class combo statuses in a very quick web search, so I'll try and provide some screenshots when I'm home this evening.
Meanwhile, if I remember correctly: Staggered is a downwards arrow-like shape, Disoriented looks a bit like a ball/gyrospoce and I'm not sure about Brittle off the top of my head.