Label decorations are used to show extra information about an item by modifying its label or icon. They can be used to obtain information about the state of an item without having to look at its properties in the Properties view or open its Properties dialog.
A number of label decorators may be available. To control which decorators are visible, go to the General > Appearance > Label Decorations preference page. This preference page provides a selectable list and description of the available decorations.