Banks,
When these signs are used they are meant to keep regular, untrained and unmonitored personnel outside of the area. As long as someone has undergone training and are badged with a dosimeter, they are allowed to be within the roped off area. The distance that they have set the signs would most likely be the minimum safe distance that anyone could get and only receive the minimum safe dosage of radiation. We use signs all the time offshore when there is a radioactive source on board for various operations.
I am not sure why there is radiation being used here and you may be right on the radiography. I would have to see more from the cameras.
-faz