I think Pear Conf had interaction consent buttons: green for "Approach me", red for "I don't want to interact with people", and I think yellow was something like "I only want to be approached by people I know."

I wouldn't conflate that with introversion/extroversion, though. I am very much an introvert but when I'm at a conference the thing I wish I could communicate is "Please start a conversation with me, because I won't start it myself!", not "Leave me alone!"