They probably do but the OP was probably busy with something to not notice or something. Still, I wonder how he/she couldn't have noticed what the machine and not know what it was.

As for the safety of these things, I'm on the fence about that. On one hand it's said that it is safe, on the other it uses radiation (albeit supposedly small amounts) and is basically a radiological device and should be operated by people trained in such fields for maintenance and such. Personally, I don't think the radiation output is so much that it would be deemed medical grade but I am worried about the cumulative effect of these machines, that is how much radiation would accumulate over a given amount of time and the doses absorbed.

Would be nice if a nuclear power plant like Three Mile Island got a hold of one of these backscatter machines under the pretense of security and studied it instead.