Photos courtesy of David Backlin (taken September 2002)
This intersection represents many in Iowa using the classic Iowa-style markers, with a circle for the state sign and the square angle-arrow signs, marking an intersection east of Hamburg at almost the southwest corner of Iowa. It's just a couple of miles from the Missouri line.
The US shield on some Iowa signs has a more "pinched" appearance than those now in use in other states. The US 275 signs in this pair of photos use that style of outline for the shield.