I don't have any information from the chip makers but my guess is the UV marking is a kind of 'lot identification'. Look at the food and drug items you buy... they all have a lot identifier in case it's necessary to trace a particular package back to the conditions that produced it. I suspect it's a way for Paul-son and others to relate a particular chip to the time and process that produced it.

As a security device, it's not worth much as anyone can buy fluorescent ink and stamp their counterfeit chip themselves.