The image above from NASA's Wide-field Infrared Survey Explorer is an example. The red object at upper left is an aging star shrouded in dust. Nevertheless, in a survey of 250,000 infrared sky sources cataloged in the 1970s, 17 "quasi-plausible" Dyson sphere signatures came up, according to Richard Carrigan of Fermilab.
It's imaginable that a super-civilization would begin a wave of colonization that spread out to neighboring solar type stars from its home base. Each offshoot would "astro-form" the colonized planetary system by constructing a Dyson sphere around the host star.
Carrigan envisions seeing "Dyson bubbles" in nearby galaxies. These would be clusters of Dyson spheres that enclosed a grouping of stars colonized by a Type II Kardashev civilization. The logic is that after you've built a backyard fence you can start to conceptualize building the Great Wall of China and still hope to gain perspective on the process, Carrigan writes.
These would be detected as anomalous dark voids in a galaxy's disk. When these voids were observed in infrared light they would glow brightly with the heat radiation from the surfaces of Dyson spheres. This would show that they are not that simply voids where solar-type stars are conspicuously missing.