What is the "checkering pattern" on my rear window

Both my '89 and '90 have this. When they manufacture 'safety' glass they sandwich a plastic layer between two layers of glass I think this is just the pattern of the plastic.
 
It's WAY more visible if you are wearing polarized sun glasses while u look at it. I thought it had gonne away by tinting my windows too, but after my gf bought me some Oakleys, I found out it was still there. It has something to do with the refraction of light between two mediums with different indices of refraction. Glass, plastic, glass makes it refract, so adding another layer of plastic (tint) makes it appear to go away. Adding yet another layer of glass (sun glasses, polarized to boot) makes it come back.

Al
 
I was told that it is the actual polarization of the rear glass for UV and Headlight glare, and it gets really visible when you wear polarized glasses.
 
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