"We have to vent heat somehow..." Yes, of course. And the heat of a star will make that heat completely invisible in comparison. The "spectra" that heat would

"We have to vent heat somehow..." Yes, of course. And the heat of a star will make that heat completely invisible in comparison. The "spectra" that heat would be vented at is infrared, which is infrared no matter the source. Say you had some gargantuan fusion power harnessing space station in deep space. lots of assumptions here about alien cultures, but this is likely the easiest to detect. They will do whatever they do with their energy, and then vent the waste heat. That heat will be infrared. What does a dim infrared source look like (if even visible at all)? It looks like a brown dwarf. But this is assuming a lot. It assumes some alien would even build brown dwarf sized space stations. We don't know if or even why they would do that.