Trouble is we moan about Councils not gritting the roads and then some idiot goes and does this, I am sure it will wash off and not have caused any permanent damage but that is not the point is it, it was either complete stupidity or something more sinister... either way a complete PITA
When you have spent £500 or so just on front rotors then someone does this it would test the patience of a saint... I hope you get something sorted, maybe a decent detailing would fit the bill, that's what I would be looking for if it was me.
I know the stable door is wide open and the horse is long gone, but if you have to park on the road why not get a car cover from Alex? The proper Nissan one he does has a thick wire and padlock which you run under the car, would stop this happeneing again and protect Saffy from bird poop too!