I didn't see Bobby, Rosie, or the fledglings in either Washington Square Park or Union Square Park today. But I did see new plant material on the fire escape Bobby and Rosie were on a few days ago.
The material included a couple of twigs:
It's not the first time the Hawks have brought twigs and other nesting material to spots other than the Bobst Library nest.
They used to bring material to a window ledge in sight of the library (starting in late August of 2012) but nothing became of that secondary location. Here is a post with lots of photos of them bringing material to that other spot. I'll keep tabs on this new location though and see if it amounts to anything.
A fellow Hawk-watcher informed me that this building is named The Cable Building. It was originally built as a power station and office space for the Metropolitan Traction Company. The link to the building brings you to a fascinating Wikipedia article about its history and significance to the city.
Views of the building and its top floor fire escape from further west:
The building was built between 1892-1894. My better half and I spent a few minutes researching this plot for fun and found a nice 1895 map showing the building and surrounding blocks.
Below is a cropped image of the map (free to publish online, courtesy of The Lionel Pincus & Princess Firyal Map Division, The New York Public Library):