[JPLeRouzic]

> If you find an infrared source but no associated visible star you’ve got a strong candidate for being a Dyson sphere

You mean like brown dwarfs?

[cgriswald]

Yes, but a Dyson sphere, even around a red dwarf, would be far more luminous in the infrared than a brown dwarf. It would also have a different spectrographic signature, and importantly its heat distribution would appear artificial.