For Upvc only
The finest grade wet and dry paper (I forget the correct grade) I did some builders cleans a while back and there was a plastic surgeon on site due to all the marks on the frames etc, I asked him for some of his magic stuff to help me, and to my supprise he gave me a sheet of wet and dry.
Make it nice and wet and run in along the length of the sill (not width ways) same for the frames, when the mark has gone give the sill a wipe down and you will see it as good as new, you can treat the sill afterwards with a wax, but I wouldn't bother with that, I did a very bad sill of my own several months back, it came up as new and just needs a wipe over like any other sill now.