In 2009 my father and my uncle found these photos -- taken by my paternal grandfather during the 1950s -- and gave them to me, knowing I would appreciate them. That was about 20 years after I had begun taking road sign photos of my own, and until then I had the mistaken notion that I was the first in my family to have this strange hobby. Is it possible that this sort of thing can be passed down through bloodlines?
Identifying the location of that last South Dakota photo was pretty complicated, and the fact that it was not a very clear shot did not help. I will start by getting to the bottom line: I believe this was taken near Chamberlain, at the Missouri River crossing (these two routes were overlapped in that area from 1939-1976, as illustrated on the 1939 USGS topo). If you dispute this, then you can read on to find out how I arrived at this conclusion, and then contact me if you have reason to believe I am mistaken on any of these points:
Today US 16 begins in Rapid City, and exists only to the west of there, into Wyoming. SD 47 is a north-south route, running down almost the exact middle of the state. So today these two routes do not intersect. However, until 1980, US 16 did continue east of Rapid City, running all the way across SD and into Minnesota, essentially along today's I-90 corridor (in fact, the reason US 16 was eliminated east of Rapid City is because I-90 replaced its functionality). So prior to 1980 these two routes did intersect (and I-90 was not built through this area until the early 1970s, so prior to that US 16 was the primary east-west route across SD). SD 47 joined US 16 near the point where the two routes crossed the Missouri River. However, this introduces another complicating factor: that of Lake Francis Case (an impoundment on the Missouri). Construction of Ft. Randall Dam began in 1946, and apparently by 1954 enough water was backed up to begin generating electric power (the entire project was completed in 1956.) The USGS Oacoma quadrangle is dated 1952 (pre-Lake Francis Case), but the Chamberlain quad was 1974 (post-lake). (Iona NW quad was also 1952, and shows the undammed Missouri River, but also indicates areas of future inundation.) The 1952 quads indicate that SD 47 was overlapped with US 16 between Oacoma and Chamberlain (US 16 crossed the Missouri via a bridge that no longer exists... well, actually it exists, but it's been moved. Today's Business Loop 90 (King Avenue) bridge is a twin truss bridge. But one of those bridges was originally about three blocks north of the present location... in fact, some of the old pilings are still there). This map also indicates the historic routing of SD 47, which went pretty much due north from Iona, on a relatively direct route to Oacoma. But part of this route was soon to be under water, so apparently it was just a few years later (by 1955) that SD 47 was changed to its current alignment (which heads more northwesterly out of Iona, towards Reliance).
The point of all this is that, if the photo was shot prior to 1955, then the only place it could've been taken was along an approx. three-mile stretch between Chamberlain and Oacoma. If it was after 1955, then it could've been anywhere between Chamberlain and Reliance (an approx. 10-mile stretch). However, there appears to be a fairly large body of water in the background. Just behind the shields there appears to be a structure - perhaps an ornamental gateway of sorts at the bridge approach, or maybe an historical marker - either of which would make sense at the location of a river crossing. The words visible on the pylon appear to say "American Island", and based on other photos I've found on the web, the full inscription was probably "American Island Park". This makes sense, because there was indeed such an island in the Missouri near Chamberlain before it was submerged by Lake Francis Case (in fact, this island is even mentioned in the 1804-1806 journals of Lewis and Clark). Elsewhere on the web I learned that there was a public park of sorts on this island, with a pool, golf course, race track, shooting range, cottages for rent, etc. Grandpa may have known that this park was soon to be lost forever... maybe that's why he took that photo.
(This area has changed a lot since this photo was taken. Today SD 47 runs along old US 16 for about 2 miles near Reliance. But this has been the case only since about 1976, and the photo was obviously taken long before then.)