From the look of the text in the editor pane you haven't told Joplin to deviate from the default body font. I guess you need an inline font style similar to:
set $ws1 "1: <font style="font-family:fontawesome;">x</font>"
where x is the character you want to display.
I do not know if the fontawesome font is called "fontawesome" for the purposes of styling as I do not use it, but hopefully you get my gist...
Edit:
Just loaded a FontAwesome font variant to test this.