Hover the mouse over the icon then it will show you more information. Open the information panel of the building, and it will tell you the problem below the title bar, with the icon on the left. It is show in a small square bubble with a icon, pulsing above the building. Notice that the happiness has gone way down.
Here is the information panel of an industrial building with not enough workers, now in the SECOND stage of the Problem (in other problems the icon would be red, but here it is still white). This problem occurs when the 'jobs available' meter is too high Here is the information panel of an industrial building with not enough workers in the first stage of the Problem. A problem is an issue that a structure of building has with the services and utilities given to it, mostly them not having enough of it, or being on fire, flooded or abandoned.
