Address numerals "107" faintly visible at the top of this rowhouse. More signage, now illegible, running vertically along the edges and between the windows.
Part of the group of buildings that are/once were part of the Trenton China Pottery Co. (other signage covered previously).
107 N 2nd Street [map]

Large letters - "... H (O or U?) E ..."
Below - "...(PA)SSYUNK Av. ABO(VE?)..."
Had this forwarded to me by a fan of the site.
Recently uncovered in a friend-of-friend's South Philly rowhome during major renovation. The owner's house was built next to a (corner?) rowhome that obviously had an advertisement on it's exterior, and it was remarkably well preserved when the walls went up next to it (much like the covered portions of this sign). The sign runs up the wall through both stories of the owner's house...
Looking at the map, it appears that at some point Wilder Street may have run through this triangular-shaped block to Point Breeze Avenue, or at least there might have been a driveway to the large space behind the houses.
UPDATE - Commenter Mike sent us this interactive map overlay website by the Greater Philadelphia GeoHistory Network, according to which, as far back as 1895 in the Philadelphia Atlas by G. W. Bromley, the area clearly shows a driveway, or at least a space, between the rowhouses opposite Wilder Street. Traffic on 21st street travels south, which would explain the desirability for a sign against this north-facing wall. Correction: Traffic at one time travelled NORTH (see comments), which makes sense as this sign faces SOUTH. See here:

I've contacted the owners to see if I can dig up anything. More information soon!
21st and Dickinson at Wilder Street (no longer visible from the outside) [map]
Not Philadelphian, but very cool. Renovations at the Notting Hill Gate tube station uncovered these midcentury posters in an abandoned hallway. The hallway used to lead to elevators, which were replaced with escalators from 1956 to 1959. These signs have been hidden away from sight for fifty years!
See more photos in this Flickr set.
Notting Hill Gate, Kensington, London [map]