This is kind of a small feature but it is useful if you have a large code base maintained by multiple teams. While you check this out you can try the other decorations available too.
I am a fan of the CVS label decorations in Eclipse. Just by looking at the file in Package Explorer I can find out whether the file is in sync with CVS. In the recent builds of Eclipse a new label decoration is available. It is called ‘Java Type Indicator’. It can be accessed via Window>Preference>General>Appearance>Label Decorations. Just check Java Type Indicator. Now the package explorer will show decorations like the ones in the screenshot for Abstract Class and Interface.