Currently it's hard to find what the indicator mean, without any label. Add a tooltip, shamelessly copied from js/ui/dash.js in core shell.
gnome-shell 3.5.90 has a new, bigger, message-tray. Restyle the systemMonitor appropriately to blend in.
https://bugzilla.gnome.org/show_bug.cgi?id=661443
https://bugzilla.gnome.org/show_bug.cgi?id=634080