In Star Trek: DS9 (Season 5, Episode 7, "Let He Who Is Without Sin..."), Worf and Jadzia visit the pleasure planet of Risa for a vacation. While there, one of Kurzon's old lovers (Arandis) recognizes Dax and they exchange pleasantries - and near the end, Arandis says
"It's so good to see you again, Dax. Your new host is very attractive."
Without having seen Jadzia before, how did she know that Jadzia was Dax?
I want to say that this has happened in the series on more than one occasion, but I don't have the references. (I know that Kurzon had a high reputation with the Klingons, but I seem to remember that they were told of Jadzia's "Dax" identity - but I might be remembering incorrectly. I figure that other Trill (like Dax's ex-wife, I can't remember the host name) don't necessarily count as they might have a way of recognizing, or at least being privy to, the fact. I'm trying to think of some other examples.)