for now from the Appearance panel in gnome control center (you need the unity version).
In case you removed it from favorites as well (i.e. cfr gsettings get com.canonical.Unity.Launcher favorites), you need to make sure that that list contains also the 'unity://expo-icon' URI.
@Marco:
for now from the Appearance panel in gnome control center (you need the unity version). Unity.Launcher favorites), you need to make sure that that list contains also the 'unity://expo-icon' URI.
In case you removed it from favorites as well (i.e. cfr gsettings get com.canonical.