So conceiably someone could have sent a signal from the other part of the lense some billion years ago and we "just" need to figure out what to listen for.
I don't think so, that would mean these "someones" would have to be developed enough to send interstellar messages through gravitational lenses when the very first solar systems and rocky planets were being formed, around 10 billion years ago. It seems too early for technology at that level.
