At the moment we couldn't see our impressive civilization from Mars. There are some hypothetical characteristics of civilizations that might have achieved a higher level of technology than ours, Dyson spheres, for example, that would alter the spectrum as seen of their central star, that could be seen from a good distance. These are big things that ought to be detectable.
What if no advanced civilization has any reason to build a Dyson sphere? My opinion is that we will never build a Dyson sphere and neither will anyone else. However grand the concept, it is nonetheless a crude and costly solution to a problem that IMO almost certainly will not exist by the time we could build one.
I'll say!
Considering that a Dyson sphere ENCAPSULATES a star and planet(s) within, it would undoubtedly affect the radiation observed from "outside". In effect, the star would (from a distant observer's POV) "fade out" over several generations.
It would merely be a "mystery of the stars" for all observers, unless and until they/we can travel there and find out what's going on.