Just heard your talk and found it quite interesting.
I am wondering if you have heard of this study
that looked at how likely is it that our solar system
would have received "junk" from other technological civilizations. "Junk" being space debris that can be anything from the spent upper stage of a rocket to say paint chips that gets ejected out of the home planetary system via some gravitational interaction,and wanders through the galaxy until it falls into our solar system. The conclusion was that there may be a fair bit of this floating around in our Solar System. The work was done by a Russian with a name something like Akripikov.