Monaco font for airline or powerline vim plugin. Which is tested on gnome terminal in Ubuntu 14.04 LTS.

• Clone or copy current files under your prefered folder
• Open terminal and change to the font directory where you downloaded files

cd /path/to/directory/which/contains/downloaded/files/font

• Move Ubuntu Mono derivative Powerline.ttf to your home folder ~/.fonts. If .fonts direcory does not exists create it (mkdir ~/.fonts)

mkdir ~/.fonts
mv Ubuntu\ Mono\ derivative\ Powerline.ttf ~/.fonts

• Change to config directory and move 10-powerline-symbols.conf to ~/.config/fontconfig/conf.d/. If folders does not exists create them

mv 10-powerline-symbols.conf ~/.config/fontconfig/conf.d/

• Execute following in terminal in order to update font cache and close all terminal windows.

sudo fc-cache

• Open gnome terminal and select Monaco for Powerline in terminal configuration window
• Open ~/.vimrc in vim and add let g:airline_powerline_fonts = 1 for enabling powerline fonts in airline

vim ~/.vimrc
let g:airline_powerline_fonts = 1

• Quit from vim and open again. Now you can see powerline symbols in your airline theme.

P.S.: I did not use powerline so I did not tested but it works in airline. If you wondering why font name Ubuntu Mono derivative Powerline.ttf read here