This little old firehouse, built in 1894 (according to the sign), has been lovingly restored as a private residence, complete with its own tower and a roof deck that must have a spectacular view. (Those yellow signs in the windows inform the world that the owner has official permission from the city to use a roof deck in his private residence.)
Update: The August 2023 Pittsburgh History and Landmarks Foundation newsletter informs us that the foundation has just awarded a Historic Lanmark plaque to this building. According to the PHLF, the architect was the prolific Charles Bickel. The architect responsible for turning it into a residence in 1982 was Sam Taylor.
On city planning maps, this part of the neighborhood is the South Side Slopes, but it is traditionally called “Arlington.”