Chicago has many block club signs. What are block clubs and what do they do?

Block club signs are all over the city, usually welcoming you to the neighborhood or telling you what you should or should not do while you’re there. A Curious City listener said they often see these signs on their way to work, and they wondered about the story behind them. What is a block club, what’s their history and who are the people involved? We visited two: the Ada United Block Club of 61st and 62nd and The Westside Block Club Association.