This might seem obvious to anyone who uses the Gnome desktop environment for Linux, but since most of you don’t, I thought it worth pointing out. In Gnome, You can put “emblems” on files or folders. The emblems are small icons that help differentiate and identify particular items. They work something like an graphical/icon version of Mac OS “labels” or GMail “labels”.
The small screenshot below shows (full-size screenshot) a few of the default emblems, and a few of my own custom emblems (the Windows and Acts of Volition icons).
There is a handy set of default emblems to start off (eg. Urgent, Web, Documents, New, Personal, Photos, etc.) and you can easily add your own custom emblems.