#!/bin/bash
#Motivated by this post on Ubuntuforums.org, I have found a solution to my issue in two steps.
#Purge and reinstall network-manager-gnome:
sudo apt-get purge network-manager-gnome
sudo apt-get install network-manager-gnome
#Add nm-applet to the Startup Applications (which may be found by entering "Startup Applications" in the Dash).
#I verified that the latter step was necessary, as the indicator did not appear after login without this addition of nm-applet to the Startup Applications.
from http://askubuntu.com/questions/159812/network-manager-indicator-missing