How do sisters in niqab recognize friends in public?

As-salamu alaykum! I'm not Muslim myself, but I had a sweet moment at the park recently with my baby girl. We were at the swings, and there was a sister in niqab (only eyes showing) pushing her little boy. She greeted me with a warm 'Hello there!' and I replied. Then she asked, 'Do you remember me from the other day?' I honestly couldn't, because in our area, many sisters wear niqab. It got me thinking: how do you recognize friends or even family when everyone's face is covered like that? Are there subtle ways you tell each other apart without speaking? I used to think niqab makes a person completely anonymous, but maybe there are tricks to make socializing easier. Would love to hear your thoughts, in sha' Allah.