http://www.debugpoint.com/2014/07/wifinetwork-icon-is-not-showing-in-ubuntu-14-04-lts/

[update 3]
As per bug report (link below) in Launchpad, it seems fixed and patch released. Did anyone tried ?
https://bugs.launchpad.net/ubuntu/+source/lxsession/+bug/1308348
[update 2]
Click here to install Gnome by replacing Unity in Ubuntu 14.04. Gnome panel will have the wifi icon.
[update 1]
See below for alternate method to connect to WIFI / wireless in Ubuntu
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So, suddenly my WIFI / Network icon from the panel is gone after installing Ubuntu 14.04 LTS in my system. I tried to manually restart the applet from the terminal – but no luck. I even tried to kick it off by manually adding it to the startup application. But still no luck.

All I get is below error.

~$ nm-applet
nm-applet-Message: using fallback from indicator to GtkStatusIcon

(nm-applet:2542): nm-applet-WARNING **: Could not find ShellVersion property on org.gnome.Shell after 5 tries
^Cnm-applet-Message: PID 0 (we are 2542) sent signal 2, shutting down...

(nm-applet:2542): GLib-CRITICAL **: Source ID 101 was not found when attempting to remove it


However – its a bug in the Ubuntu 14.04 LTS and being worked upon as of today. You can get a details of the bug here – https://bugs.launchpad.net/ubuntu/+source/lxsession/+bug/1308348

Alternate Method to Connect to wifi

There is an alternate method to see the list of wifi (wireless) networks available and to connect them even if the nm-applet icon not available. To do this follow below steps –

a. Go to Unity SEARCH and type “net”, you will see “Network” listed. Click on “Network” as below.

b. After you click, in opened network window you can see list of available wifi networks. Click the “>” icon beside your own wifi network.

c. Click Connect button to connect to WIFI.

e. Thats it! You should be connected.

Drop a comment if it solves your problem.