Mate , as an ex car valeter , I highly recommend you use a window razor.
Theyre like blades for stanley knives, and come in similar packaging and can be bought very cheaply in most diy stores.
Keep the razor flat on the window and it gets all the crap off without scratching the glass.
Dont use it on lights or paintwork tho , as itll work like a potato peeler !!
Once youve used the razor then use the glass polish or some alcohol based cleaner to get the remnants off.
Hope that helps fella