Chris,
I have been studying UV marks for over 15 years. I have no idea which manufacturer started it; but I use it to differentiate 2 identical chips (except for UVs). This usually indicates a reissue by the manufacturer.

It is also helpful when variations of the same chip are difficult to see with the naked eye, but have 2 different UVs.

Those of us that use UVs to differentiate chips owe it all to Greg Susong, the Founder of the Chip Guide. He started the process back when he published his first book on chips.

Several years ago, I gave a seminar at the Annual Convention on UVs and how to include them in your identification/description of a chip.