Pointing to Arkansas via Route AR

Route AR near the Arkansas state line at Bakersfield, Mo.
Photo courtesy of David Backlin (taken July 2002)

This is an unusual Missouri sign assembly for a couple of reasons. First of all, when there are three markers on an assembly, they're usually in a triangular configuration (like this). In this case, the AR sign and arrow almost appear to be an afterthought. Route AR was added to the supplemental road system sometime during the 1990s, judging by official state road maps. It's a short spur to Arkansas route 87 just south of Bakersfield. Does the AR designation refer to Arkansas?