I showed the listing to my mom, who immediately said that it must stand for United States Army! She then pointed out others on the page listed with "USN" (Navy). I checked my files and, sure enough, Uncle Doyle joined the Army on 6 Oct 1942 at Fort Jackson in Columbia, SC.
I then noticed how very many men in the directory had USA, USN or USMC listed as their occupation. With WWII well under way at this point, it makes sense that so many men would be in the military - but it's another thing to look through a city directory and see the names of those men (and women). So many! It really shows how many folks were affected by the war and makes me wonder how life in this town was affected. I wonder how a person might feel to be looking through the directory and see their spouse's name listed with there own, while they were actually half-way around the world. It makes me sad to think of it.
In the abbreviations section, the different military abbreviations are listed, though I imagine no one would have needed to look up these particular abbreviations at the time!
Also, under "U" (United States Government), interested individuals could find out where to sign up for their military unit of choice and find the listing of the local Army Air Force Base.
And proof of World War II wasn't limited just to official government and civilian listing. Throughout the directory, there was proof of the war effort in advertisements. Patriotism was at an all time high, and you could "take a direct part in building the defenses of your country" by purchasing War Bonds, "needed so urgently for Victory."
Images and information from Hill’s Greenville (Greenville County, SC) City Directory 1943-1944, Hill Directory Co., Inc., Richmond, VA., Ancestry.com