It would take a laser of enormous power, even if it were pulsed, to be detected over lightyears distance. How long would such a system have to be operating, waiting for a species to evolve and develop the ability to detect it? A billion years? Fat chance.

I think we are more likely to discover signs of much more advanced civilization, capable of disturbing the orbits of planets, or one that has moved in closer to its native star to collect more energy. We may detect exotic molecular spectra in a star's corona, stuff that shouldn't be there.... like DNA. That'd be pretty good evidence of ET.