Sitting opposite on Brighton-bound train in a group of 3 American girls

We sat opposite each other in a train heading to Brighton between London Bridge and East Croydon in the morning of the 17th September. You were a North American girl in a company of other 2. I was wearing a plain white T-shirt under a black coat. I never made an approach, but you said “have a nice day” when I was about to get off at East Croydon. I may owe you a coffee.