It's a yellow placard put on tables up and down the country to encourage people to have conversations over coffee, started by a new mom who was sat observing people in coffee shops and wondered who would welcome a friendly chat over a coffee, they have a website it's well worth looking at especially if you are looking to chat or make new friends for whatever reason.
They also do a weekly phone call to people experiencing loneliness,
The online coffee chat is 30 minutes twice a week on zoom, I have really enjoyed it the last couple of weeks, it's lifted my wellbeing