Andre Torrez has a cute and simple recipe for making your shell prompt into a hamburger (or other whimsical emoji character). Just type
export PS1="\w 🍔 "
into the terminal to try it out. Apparently some Macs ship with an Emoji font installed; if you need one, you can get a free, excellent one from the Unicode Fonts for Ancient Scripts page, by downloading the Symbola font (.ZIP file) and installing it with your font manager.
To make the change permanent, you need to add a line to .profile, .bash_profile or .bashrc (depending on your *nix flavor). There are lots of other ways to customize your prompt enumerated in the article, too.
