Apple's text replacement feature is perfect for this. I have a bunch of ascii emojis that auto-complete for me when I type a matching string (I've based mine on the old BB Code emoticon syntax[1]), e.g. :shrug: → ¯\\(ツ)/¯ (as it happens I also have a text replacement that converts -> into an arrow).

[1] https://tl.net/forum/smilies.php