I don’t know the circumstances, but I would have tried to make eye contact and just blatantly stare at them for minutes straight, maybe even hamming it up with a look of slight unhinged interest. They would have become more uncomfortable and might have started being anxious that a stranger is eavesdropping on them, causing them to want to be more discrete, depending on their disposition. I’ve actually tried this before, and it seems to sometimes work if they can see you staring at them. Give a subtle, slight grin, like you might be sexually turned on. If you won’t see them again then it’s worth a try.
I don’t know the circumstances, but I would have tried to make eye contact and just blatantly stare at them for minutes straight, maybe even hamming it up with a look of slight unhinged interest. They would have become more uncomfortable and might have started being anxious that a stranger is eavesdropping on them, causing them to want to be more discrete, depending on their disposition. I’ve actually tried this before, and it seems to sometimes work if they can see you staring at them. Give a subtle, slight grin, like you might be sexually turned on. If you won’t see them again then it’s worth a try.