I have never tried this on a glass but, I know Easy-Off (the oven cleaner, not the as seen on tv crap with the terrible infomercial) takes lettering off of vehicles without damaging the clear coat. You just spray it on and apply a little heat. A blow dryer works a heat gun is better. After a few mins the lettering just wipes away. Its safer than acid too. PS I lived in Portland for a few years before my work moved me to Maine. My wife and I miss Oregon and would love to get back. Go Ducks!