echo $'<Multi_key> <m> <o> <j> <o> : "\U1F525"  U1F525 # FIRE' >>~/.XCompose

I'm not personally a fan of emoji, but I do like using and typing more than plain ASCII in the terminal. (One thing I liked about Julia is their partial embrace of Unicode, and one thing I don't is that you can't write lambdas with ‘↦’.)