On Fri, 23 Sep 2005 22:03:09 GMT, Korbin Dallas
said in rec.radio.scanner:

I have rented some GM models lately that have someone in the Window Tint
that is blocking RF. I cant use my XM radio & GPS sitting on the dash in
there new vehicles. I would suspect this would have a similar effect on
Glass mount Antennas...

Some cars - I don't know about GM - have a clear spot, about 2" on a
side, at the top center of the rear window - to mount an on-glass cell
phone antenna. Since it's clear glass, you can mount any on-glass
antenna you like there.