I suspect the main difference between the US and UK this way is the honesty of the process. In the US a ton of money an energy is spent on social signalling and class definition, but also on maintaining a fiction that "class" isn't really a thing.

I do think the US class system is easier to fake, as it relies a bit more on superficial signifiers than institutions and history than the UK. The myth of the "self made man" is also held dear, so you can do ok if you play to that story; you'll still may never really belong but your kids probably will.

Second login with my throwaway account today! Apologies in advance: This stuff is much too personal to post under my real identity.

Exactly this, in my experience. I am from a upper-middle-class family. I live in East Asia now, and wealthy by local standards. Whenever I travel to developing countries in Asia, I am regularly reminded of my upper-middle-class-plus-plus status by the straightness and whiteness of my teeth! Yes, literally, I can count on many, many hands how many times random strangers approach me on the street/bus/train/hotel/airport in developing countries with comments about my straight and/or white teeth. (Please: Do not read humble-brag into that.)

Could we, perhaps, say that accent is a big social divide in UK, whereas teeth are a big social divide in US? I would love to hear from Canadians, Kiwis, Aussies, Saffers, etc...(anyone!) about experiences in their home culture.