A loose brick reveals ROSE

On a survey of the second floor roof, I noticed a brick had been pulled out of the elevator penthouse. The stamp on the brick says ROSE. 

Let this brick collector site (here's another) tell you all about it.

The history of Roseton, the "ghost town" of the Rose Brick Company

The Rose brick

Missing brick cavity

The skin is flaking off the brick here

The 1916 elevator and staircase tower, made of Rose bricks