I taught at one of the best private schools in Great Britain for a while, so I consider myself qualified to give a definitive answer:
Tweed.
Seriously: In my ten years as a teacher, I never once saw a single tweed tea towel, but when I started working in private education, the damned stuff was suddenly everywhere. The teachers wore tweed (and the teachers were almost without exception "old boys" or "old girls" whose parents could comfortably afford twice what most people earn in a year to keep their children out of circulation for most of the year), the staff wore tweed, and the parents were almost constantly dressed in tweed. I swear, some of them slept in tweed pajamas.
If they weren't wearing tweed, they were playing peasants for some reason or other. It didn't matter whether they lived somewhere in the Cotswolds or in the heart of London. Their peasant outfits were sometimes a little worn, but always unnaturally clean.
So if I see someone in the middle of town wearing tweed or peasant clothes who has never been closer than half a mile to a cow, then I know I'm dealing with the fourteenth Lord Bonkingly-Spinkle or something like that.
EDIT: Several people have pointed out to me that tweed is a country thing, not a city thing. Being about as aristocratic as Derek Trotter and having never owned a piece of tweed in my life, I don't know, but it's worth mentioning that the school where I worked was in the countryside.
Apart from that, during COVID all our meetings with the parents were remote, and they still wore tweed and farm clothes, no matter where they lived.