I kind of liked your idea for searching for ET by "looking down." The particular details re tuning forks were stupid, but... I think it is an interesting idea in the abstract that the aliens would want to "leave a message" so that they would be heard at any time in the future, not just one time like the stupid idea of sending a radio message once. Also, I point out that this idea was already in Arthur Clarke's "2001" sci-fi. His aliens left a monolith made of magic indestructible material on the moon, etc. Having said that, the question is how should the aliens act, and how should we act? Seems to me, the Moon is a lot better place to leave a message than Earth. It'd last longer. Perhaps a satellite in Earth orbit would be even longer lasting, and anyhow very easy to spot. As far as I understand they claim to be tracking everything in orbit larger than X, where X is what? The size of a golf ball? And nothing was there? Certainly a golf ball sized satellite would be adequate to carry an enormous amount of info from aliens, terabytes easily. How long would it last? Supposedly the layer of dust on the moon is only about 2 cm thick, suggesting that if you are willing to sacrifice an outer layer a few cm thick your satellite has decent odds of lasting a few Gyears? And dust particles in space obviously do last for Gyears in the sense of not evaporating, so you're safe against that. So... I doubt ET left any messages for us.