A flag can be attached to a model or result. As with colors, flags can indicate, e.g., key runs, good runs, or bad runs, but of course the meaning of the flags is all up to the user.
To assign a flag to a model or result in the model overview:
Select the model or result in the list.
Click 
in the toolbar and select the desired flag from the popup.
Or
Right-click the selected model or result and choose the desired flag from the Colors & flags submenu.