Funnily enough, I published a Python library two days ago that uses emojis to indicate where certain non-msgpackable builtin types have been forced into msgpackable objects: https://github.com/umarbutler/persist-cache/blob/main/src/pe...

is used for tuples, for sets, for frozen sets, for pickles, for bytes and for bytearrays.

I thought it was pretty ingenious but clearly I’m not the only one to think of it.