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To alter Earth's signature as seen by an alien version of Kepler, a laser system would have to emit 30 megawatts of power for about 10 hours per year, coinciding with Earth's passing in front of the sun, the duo calculated.
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Concealing Earth's existence from extraterrestrials, or announcing its presence with an artificial light curve, would work only if humanity knew or suspected where those aliens were living.

Why did it take so long for that following paragraph to show up? You don't know which side of the sun is the "front", and you don't know if any alien civilizations exist, let alone where they are. Assuming the existence of such civilizations, by the time we find them, it is too late to think about hiding from them. On the other hand, by the time we find them, they are likely already hidden in the distant past, since the starlight that reaches Earth is a view into the past. We have no way of knowing what the universe looks like at this moment.

Silly idea, better suited for a science fiction novel than a scientific thought experiment.