To toggle class and job icons for party or alliance members in the chat log, select System from the main menu and open the Character Configuration menu, then select the Log Window Settings tab from the column on the left. Under General, select Name Display Settings. Checking the "Class/Job" box under "Display icons for classes, jobs, and roles in the chat log." will display class or job icons, while checking the "Role" box will display each player's corresponding role icon.

A preview of your selected settings will also be displayed at the bottom of the window.