Set the icon of a system folder in GNOME

By the default, unlike Windows, the icon of Dropbox folder in Linux is the same as other normal folder. To change icon to, you may type the command:

gvfs-set-attribute ~/Dropbox metadata::custom-icon-name folder-dropbox

Ref: http://oxygene.sk/2012/10/dropbox-folder-icon-in-gnome-3/