Ubuntu 14 fixing fonts for agnoster
I encounter the same problem and the fonts-powerline package was missing.
A sudo apt-get install fonts-powerline should solve the problem.
you should install Menlo-Powerline font patch to ~/.fonts/: https://gist.github.com/qrush/1595572/raw/417a3fa36e35ca91d6d23ac961071094c26e5fad/Menlo-Powerline.otf