On my s1000 I have it in a circular waterproof cyclinder, which is attached to the back of the number plate and thread locked. Not massively secure, but I don't leave the bike out much. On my other bike I keep the tax disc in a drawer, and the original tax discs rom when I first got the bike is in a manky unreadable tax disc holder attached to the front forks. Never had any issues....
Local IAM group keep telling me the s1's tax disc is not in a legal place, but local police often look over the bike when I'm parked in a cafe, and they only ever want to chat about the bikes performance.........
I would never put a tax disc in the windshield as it doesn't look good. I was actually quite taken aback when I collected the s1000 (brand new) and the dealer expected me to put it there and didn't even provide a cheap holder for the forks....