It is actually a rear cable hanger designed for being used with the seat binder bolt, it i made by Tektro:
http://www.amazon.com/Tektro-Rear-Cable ... B001CJV94OI have been using this setup for 3 or 4 years now, it is still going strong and working well. I had to modify the top loop of the hanger a bit so that it didn't interfere with bar on Thomson stem. It tends to pull a bit to one side because its hard to center, so I had to slightly compensate by increasing the spring tension on my Neo-Retro's to keep the pads centred on rims, easy fix though!
Has a pretty clean/minimal look in the end. I ended up going this route due to lack of steer tube to run a normal hanger. My options were, drill out stem (wasn't quite prepared to do that), or run one of those heavy and kind of ugly crown mounted ones. This was only $2-$3 to try out, so I went this route and it worked.