Cool find. I wonder if this could be the realization of dda's "clone stamp" theory, where, rather than do a lousy job blurring over sensitive sites, they clone stamp actual buildings, or the surrounding environment, to make the omissions less obvious. "Annonymous Tourist Building Footprint" could be the cartographer's notes as to the desired look of the obscured building, not intending it to be read by the general public. Possible?
If you zoom out you'll see the comment/label moves around a bit. It doesn't stay over that particular building, so I'm not sure where exactly it's supposed to be.
There's been a lot of development in that part of London over the past few years. I suspect a cartographer is making an editorial comment on the new architecture of the area.
![Pin on Pinterest](https://pinterest.com/pin/create/link/?url=https%3A%2F%2Fvirtualglobetrotting.com%2Fmap%2Freserved-anonymous-tourist-building-footprint%2F&media=https%3A%2F%2Fc2.vgtstatic.com%2Fthumbll%2F2%2F4%2F24746-v1%2Freserved-anonymous-tourist-building-footprint.jpg&description="{RESERVED} Anonymous Tourist Building Footprint"){kind=small}
No Longer There 
It's wrote with the same color than the district zones...
There's been a lot of development in that part of London over the past few years. I suspect a cartographer is making an editorial comment on the new architecture of the area.