I live in a gentrifying neighbourhood in Montreal and crack is a thing.

The semi-homeless people who crash at the clinic in front of me are highly animated, talking to themselves loudly etc. for a few days after the provincial welfare cheques go out. Then it's all quiet.

It's the only neighbourhood in North America, where regular looking, polite folks come up asking for 'spare change' all the time.

Also - crack has a specific odour.