for the love of god please don't. the yubikey-agent example provided exemplifies everything i dislike about github READMEs and whimsical user interfaces.
on the technical side, symbols and emojis can render inconsistently among terminals, leading to potentially confusing messaging. on the artistic side, personal tolerances towards whimsy and playfulness vary wildly and should only be used very sparingly and ONLY if you know what you're doing (if you have to ask, you probably don't)