Intellij marks files that contain errors (and the containers for those files) using the red squiggle underline. This indicator shows up in the breadcrumb view, the editor tab title, and the project view.
This is great, but I'm not always working with the project view showing. It would be even better if the indicator was shown in other views that show file names. The one in particular that I noticed was the Hierarchy view, but really any view that shows filenames should support this indicator, such as the Structure view, the search results view, etc.
This feature has been in eclipse for a while, so I'm hoping it's in Intellij too and I just haven't found it yet.