DNEWS VIDEO: ALIEN SPECULATION
The bottom line is that asteroid systems may be as diverse and unusual as the planetary systems they inhabit. Therefore, anomalies alone could not conclusively prove the existence of alien asteroid miners. Finding an oddball-looking asteroid belt might be suggestive of astroengineering, but it certainly would not prove it.
An intense program of SETI follow-up observations might look for telecommunications leak-off signals, or there may be searches for Earth-sized planets in habitable zones near the asteroid belt. Nevertheless, SETT may be the most practical and fastest strategy for finding advanced life off Earth.
It will be two decades or more before we have large-enough space telescopes to survey nearby exoplanets and looks for biomarkers. And those data will not give a clue as to how evolved the native life is.
A space colonizing civilization, maybe no more than a millennium advanced from us, must be doing something ambitious that we can notice from light-years away with modest-sized telescopes. Maybe the evidence is already in our astronomical archives; we simply don't recognize it, yet.