What kind of “directional” signal you can think of sending from a planet millions years ago that can hit earth exactly in the moment a SETI antenna directed at

What kind of “directional” signal you can think of sending from a planet millions years ago that can hit earth exactly in the moment a SETI antenna directed at it and ready to receive? And how much energy should this civilization keep pumping in the signal to increase the probability that someone can receive them? And why it should make any sense to waste energy like this when the probability that you can receive a confirmation is equal zero even when other civilizations are out there? About the required power and signal degradation over distance, see this: https://www.quora.com/How-far-do-radio-signals-travel-into-space-before-they-degrade-to-a-degree-beyond-being-possible-to-be-detected https://www.quora.com/How-far-do-radio-signals-travel-into-s...