The Clarke Exobelt is the name that Dr Hector Socas-Navarro has given to perhaps the largest structure humans have built. A collection of satellites in earth orbit (geosynchronous) 36,000 km radius. All circling the earth at the same speed in the same direction. The density of this orbit has been increasing since the 1960s but is not yet sufficiently dense for detection from interstellar distances. But in 200 years it may be. In the meantime, this concept works the other way around too. SETI researchers can search for these megastructures or Tecno Signatures to look for extraterrestrial intelligence