Sherlock Holmes Museum in Westminster

You're standing at the Sherlock Holmes Museum on Baker Street in London, close to Regent's Park. Look at the front of the building. There's a blue plaque reading 221b, Sherlock Holmes, Consulting Detective, 1881 to 1904. It looks just like the official blue plaques London puts on the homes of famous residents. But the organisation behind those has nothing to do with this one.