Lovely video....Yes, As soon as you reach Khab Bridge to ascend for Kahzigs and Nako, the Board says Welcome to Hangrang valley.
In my video, starting at 6 min mark you can find the Board at Khab bridge.
One saw a fair amount of vehicles coming from the opposite side.
Spiti has become a pretty popular destination.
My first visit was in 2004 and the desolation that one experienced as we were ascending the Kazigs was something else.
In 2012, the new Khab bridge was operational. The old bridge was still in place. I don't see the old bridge now.