As promised. This is from my 2004 A6. Rear glass..

Hope this will help.

 

See I have a 1998. I hope they are the same, but I dont think that a Audi dealer would sell a car with a non factory window.

 

The only similar thing I have seen is on front windows with de-frosters. They come with very thin squiggly lines. An option is cold European countries, and the UK.

The faint lines on front de-frosting windows make them pretty expensive, hence they don't use them on rear windows.

Since you have what looks like a part number, see what part description you get from the dealer. It might be something like, rear heated windscreen (near invesible heater elements)...

Does look great though.... [8D]

Another question, does it actually work?

 

Well it does seem to work...I live in OK so cannot really tell. But it does get rid of the fog on the rear window.

 

OK...those lines in the window are the defroster. Got that cleared up from Audi.