As far as the Post Office is concerned, Dormont is “Pittsburgh,” as is everything with a 152– ZIP code. This dignified post office is typical of many branches built in the Franklin Roosevelt era. The bronze lanterns are especially fine.
The cornerstone lists the supervising architect, the supervising engineer, and the architect. Louis A. Simon was responsible for many federal projects; he created standard plans that would then be adapted by other architects to the individual situation. Carroll H. Pratt seems to have been a New York architect who, aside from Rooseveltian post offices like this one, designed homes for the wealthy.
Now here is a little bit of Pittsburgh lore too arcane for most Pittsburghers, but not for old Pa Pitt. Before there were ZIP codes, there were postal codes in big cities that referred to the individual postal station. A letter going to the South Hills in Pittsburgh, for example, would be addressed to Pittsburgh 16. When ZIP codes were assigned, the old Pittsburgh postal codes were retained as the last two digits, so that Pittsburgh 16 became ZIP code 15216.
Those old postal codes were in alphabetical order, so the original ZIP codes for Pittsburgh are also in alphabetical order. Of course you have to know the names of the branch post offices to decipher the order. For example, Lawrenceville was Pittsburgh 1 (now 15201), because it is Arsenal station to the post office. The South Side was Pittsburgh 3 (15203), because it is Carson station. Pittsburgh 21, Wilkinsburg, was the last in the series; ZIP codes 15222 and above are later creations.