Install Powerline fonts for Z shell
Please note: there is an APT package called "fonts-powerline" which is tested and working for Ubuntu 20.04 which achieves the same outcome. Try "sudo apt install fonts-powerline"
If you're using Z Shell and a special prompt theme designed with Powerline fonts in mind, you'll need to install them on your machine. These are the most clear and cut-down instructions that I've found to work with Ubuntu 16.10 (also confirmed working for 17.04, 17.10, 18.04, 19.10) and all credit goes to renshuki's Ubuntu 14.04 + Terminator + Oh My ZSH with Agnoster Theme gist. I've extracted just the Powerline font instructions - my personal setup uses Prezto instead of Oh My ZSH (not included here).
Get the font and config files