In the Culture universe of Iain M Banks, there is a short story where a GSV scouts out contemporary Earth. The ship stays out of sight until it's time to leave

In the Culture universe of Iain M Banks, there is a short story where a GSV scouts out contemporary Earth. The ship stays out of sight until it's time to leave our solar system, at which point the (mischievous) Mind leaves an EM signature for us to puzzle over. So, a zoo but a zookeeper flashes us a high five as he departs for his next adventure.