It's been observed in sonic black holes, which are mathematical analogs of gravitational black holes in fluids (though to be fair the experiment has been disputed, so the evidence is not absolutely unambiguous):
I don't have the background to be confident about this, but aren't the predicates on which Hawking Radiation is based on part of the equivalency framework between sonic and "real" black holes?
If so, then while the observation of Hawking radiation in the model is certainly interesting, calling it an observation of Hawking radiation with regards to real black holes sounds like a stretch.