When Ben Matlock leaves the ransom money at the drop site, a reassurance road sign for US-421 is clearly seen in the near background shot. US-421 is a highway that runs for almost 950 miles, from the North Carolina coast northwestward to Michigan City, Indiana where it ends at US-20. At no point does the route run within 200 miles of Georgia at all, let alone within the Atlanta vicinity.
The sign is for Georgia State Road 42 which does run near Atlanta. Not US-421 as originally reported.