In the early 1990s I was gifted a Brompton. Back then on the few times I saw anyone on another Brompton pass by, it was almost like meeting a long lost relative. There wasn't just a nod of the head or ding of the bell but stopping to chew the fat for a while! Things can be very different today.
There are so many Brompton bike out there. If for example, you were cycling through Hyde Park either end of rush hour - and quire possibly in between - you will see lots of them. Some people ding their bells, others say hello, some nod their heads as they go past and many are either oblivious or don't care about such things.
For me personally it does depend on what I am doing. If it on my commute I rarely acknowledge other Brompton riders. If however it is when I am on one of my Brompton adventures, I do.
If you have a Brompton what do you do?
Stay safe out there people!!