Earth is dotted with many humongous, human-made structures. To an alien eye, they may be tell-tale signs of intelligent goings-on, betraying our existence and hinting at our capabilities.

Making contact with ET? Aliens may already know we're here

Source: space
Source Link: https://www.space.com/space-exploration/search-for-life/making-contact-with-et-aliens-may-already-know-were-here