I've had problems with the thugs around my way as well, I had to park my Granada Cosworth round the corner for a few days, due to no parking places in my street (a long story involving a CPZ), and just look what awaited me on my return!

The offending item

Shot from inside the car.
Thankfully, I have managed to get a replacement glass for it now, but I would dearly love to get my hands on the little gits that did it! I think I would like to be wearing my steel-toecapped boots at the time!
Roy.