If you have installed Skype in Ubuntu, you will notice that it doesn’t come with an indicator displayed in the system tray. Use this method to install Skype instead:
In the terminal, type:
sudo add-apt-repository "deb http://archive.canonical.com/ $(lsb_release -sc) partner" sudo apt-get update sudo apt-get install skype && sudo apt-get -f install
This will install Skype together with its appindicator.