What does the United Nations flag have to do with a flat Earth theory? Lots apparently. Take a look at the Flat Earth Society Forum's FAQ. Yes, there are people who hold on to that belief. The UN logo closely resembles the map of the Earth proposed by the society and it is also used as evidence of a conspiracy to cover up the truth.
I stumbled upon the site when I was looking up DiscWorld on the Net. I just finished my first Disworld novel (Thud!) and I'm hooked. Explore the portal on Wikipedia to get a taste of what the books are about.