Dyson Spheres
The Dyson Sphere is an interesting idea, but when you think about it, the concept is similar to a caveman imagining that a future advanced civilization may have campfires a hundred feet high to keep entire villages warm.
There are more convenient ways for a solar-system-wide civilization to generate energy than trying to grab every last bit of sunlight.
A more plausible scenario is millions of small sources in a solar system, each radiating some heat. The total of this radiation may create an infrared signature, but it might be lost in the glare of an unconfined sun.