Photos 1 & 2 are magnifications of Photo 3 to provide additional detail of the Mail Pouch sign and the surrounding environment to enable approximate location.
Photo 4 is a Google Earth street view taken in approximately the same location as Photos 1-3 were taken, looking west.
The GPS coordinates are approximate; however, close. An inspection of the map below, in the satellite image, will show that the Mail Pouch sign would fall in deep center field at PNC Park, the home of the Pittsburgh pirates.
The Maps A & B have been used to determine the location of the Mail Pouch sign. Review of Map A will show the location of River Ave. and Sandusky St. Apparent in the view are the RR tracks, including the two spurs which turn north; and the United Storage Co. Building with it's tower appendage on the south side. The buildings beyond, in Photo 3 are visible and it is apparent that the Mail Pouch sign is on a building in a further block, beyond Federal St. Map B shows Federal St. and an inspection of Photo 1 shows the furthest building, in the distance extending to the left almost to the river. The building with the MP sign is obviously the Freight Depot Building.
This was very unique sign. It was obviously lighted from the front with spot lights and the arrangement of the cowboy's lariat suggests that the lariat was lighted and perhaps sequenced to give the impression, at night, that the lariat was being twirled above the cowboy's head. This would have been very visible from the greater Pittsburgh downtown area on the south side of the Allegheny River.