(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fimg441.imageshack.us%2Fimg441%2F4327%2Fnm20digitalstop.jpg&hash=fbd29e7e80ce808eb8f9951058073ef20dde860c)
This is at a commuter rail park/ride in a Fort Worth suburb. I've not seen unofficial city guide signage with QR codes before.
From what I can tell of the article http://www.dallasnews.com/news/community-news/tarrant-county/headlines/20120101-richland-hills-goes-high-tech-to-spread-city-information.ece?action=reregister
(yes, the Dallas paper hides behind a "paywall")
the city isn't trying to use these as actual traffic control or guide signs, but putting them in an octagon shape does give off a bit of "traffic control" feeling. At the same time, the movement is growing to restrict cell phone usage, especially texting, while driving. Hopefully these 'signs' won't be where people stop in the street to try to scan the QR codes.
given they are octagon - which is deliberately exclusively used for STOP signs to make them stand out, maybe people will stop...
I foresee a problem with the MUTCD on these.
On the topic of mis-used shapes, on Jersey Shore, I noticed that Seaside Hieghts, NJ uses white diamond-shaped signs for parking, I couldn't read them, but I believe they were for street parking pay stations.