Hope you solve your glass pecking problem. Lots of good ideas here for deterrents. I would try the owl picture or hanging curtains as Jan did.
We don't have a glass pecking problem, but we did have a coo coo wood pecker visit us one year. We live in the woods - lots of trees. No, this wood pecker had to peck at the metal cap on our chimney! After doing this for a couple of weeks, I think he finally got the idea that he wasn't going to get any bugs from the chimney, nor was he going to attract a mate - unless she was into "heavy metal".