Ambient signifiers are not a new idea in design (mostly talked about in the use of alerts), but knowing just enough about who is present would be more compellin

Ambient signifiers are not a new idea in design (mostly talked about in the use of alerts), but knowing just enough about who is present would be more compelling if there was a more clearly stated payoff for it. The idea seems to have different outcomes depending on what features the "presence" has (fuzzy cursors vs commenting at the side, for example).