I come from a long line of the downwardly mobile and my late mother had a wonderful range of sartorial social markers for commoness, such as:
For men: suede shoes worn in town, tweed (unless in the country), brown shoes with blue suits, cravats, check jackets (bookies' jackets, according to ma), sports shoes of any description (unless playing said sport), shirts that weren't cotton, loud ties, shorts unless playing sport or on a beach, white socks ...
for women: visible underwear, including VPL and black bras under light tops, stiletto heels, ankle straps on shoes, wearing black unless at a funeral, low-cut tops (acceptable only in evening or cocktail dresses), party dresses at the races, and, my personal favourite, going out without stockings before Henley.
It was really important that I knew all these rules, given that I grew up on the biggest, roughest council estate in Croydon.