Probably seeing a lot of new/upper segment cars and well maintained houses.
It is a reasonable response to high-crime areas, and it is unusual for the wealthiest parts of a city to be high-crime areas. But an area being less affluent doesn't make an area high-crime.
If you look at the other comments you can see people are actually keying off how much of a sense of community and civic pride there is in an area, as well as commercial activity. Which is going to probably distinguish between upper and lower class - even that isn't certain - but that isn't actually relevant to the topic because there is always going to be an upper and lower class. It isn't going to get a great read on how affluent they are at any given moment.
> There's a reason your original post is a very light shade of gray.
In an academic sense, yes. But no-one knows what it is - some people might be in your shoes where they read "affluent", misinterpreted it and had a fear response. Or they might have other opinions as some of the other comments lay out. Or there could have been other reasons.
One of the philosophical underpinnings of HN is that downvotes don't contain a lot of information and are a poor tool for promoting discussion - it is a wonderfully mature approach to moderation.
You'll notice my response to the thread going long was more arguments. It keeps the discussion more respectful when people only push on when they have arguments to make. Not the only option, but insinuation specifically is a weak long term strategy. As are insults, for that matter.
How well upkept are the buildings? Are they clean and well maintained or are they dingy and broken with overgrowth? Are there a lot of open shops around? Do people seem to be buying things? What kind of clothes are the people wearing? Does it seem like many people are homeless? How is the state of the transit (both public and private?) Do people feel the need to have bars on their windows and security stationed around to prevent theft, or do storefronts feel safe enough to even have merchandise sitting out? Are people eating in restaurants? Are those expensive or cheap restaurants? Do people seem to be comfortable spending a night out on the town, going to bars and shows or are the streets empty because people can't afford outside entertainment?
You can find relative class status of an area by the number of beggars, I grant you that. But you aren't going to get a bead on the actual affluence of the high-class people. Are they thousandairs or billionairs? All we really know is they aren't beggars.