Mike Williams wrote:

Wasn't it Paul Bramscher who wrote:

So it may be that larger clusters of intelligence (large cities) will be one of the earlier potentially remote-sensible artifacts of intelligence.  For example, cities might be approached as (often, in today's modern sense) having some signature (chemical, albedo, geometric, etc.) which make them often stand out.

We may never be able to pick out an alien's brain waves, but we just might detect a city on an earthlike planet in the next century or two...

That's a rather anthropomorphic concept of aliens. I'd guess that most
intelligent civilisations wouldn't build cities.

Why?  Intelligent, mammalian and non-mammalian cooperative life on Earth  all developed along social considerations.  Herds, tribes, cities, hives, etc.  Clusters or communities may be better hallmarks (though not exclusive) of intelligence and cooperation than most.

In any case, we should first go by life as we know it on earth, not some hypothetical alternative.