All photos courtesy Lou Corsaro until after the video (which is also Lou's).
The North shield is definitely older than the South shield, and the second photo shows typical Tennessee directional signage at an intersection. That's much more efficient than having separate NORTH and SOUTH banners and arrows, or even worse, separate shields. Compared to the TN 418 shields below, you can see these southbound specimens are too squat.
Northbound non-compliance from TnDOT. The signs aren't supposed to match the signal, because red is reserved for the critical STOP, DO NOT ENTER, and WRONG WAY signs. They should be black on white.
In 2007, the north end of TN (secondary) 418 was TN 91, which heads west with US 421 on what's technically a wrong-way multiplex. TN 91 was rerouted around the north side of Mountain City on the bypass seen here, missing a SOUTH 91 shield for straight ahead. I thought TN 418 would more than double in length to cover the gap, but instead it was just routed west back to US 421 and the rest of TN 91 was decommissioned.
Southbound (eastward) across South Holston Lake. It's a manmade lake, so this bridge is really the best part of it. (Lou was also there during a bad drought, and it wouldn't do the scenery justice.)
Far shot from the northeast shore of the lake.
Click to drive northbound (westward) across the lake with Lou.
These go here, taken on State St. EB (former US 421 SB) in Bristol; State St. WB is in Virginia, and all the other Bristol photos are on the Virginia page, along with a detailed description of US 421's history in that city. So follow the link below to stay with this route. Former Pennsylvania Ave. is now MLK Blvd., and here's where it hits the state line. The circles mean different things on each sign, which is a bad idea - on top, it's showing sides of the border; on the bottom, it's showing the street runs in both states at once. There's a daytime version of the state line sign (looking east from US 421) on my Virginia page, but I didn't take that one.
Modern US 421 SB crosses the border on Commonwealth Ave. with US 11E/19.