Here is a website with more information:
www.doityourself.com/stry/poisonous-plants-the-dangers-of-mountain-laurel-flowers

Plus, some of the children who had the flowers were quite young and one woman had the blossoms wrapped around her infant's toy. These kids may stick the flowers in their mouth and their parents wouldn't worry because they were told the plant was harmless. Perhaps signs aren't the solution. After all, people should know not to pick flowers in a park, but I was truly concerned for the kids.