Believe it or not, we tried this on two Vipers that had murdered numerous cones at a series of autocrosses a couple years ago: RainX. Yep, the stuff you put on your windshield did a surprisingly good job of removing just about all of the black scuff marks from those cones. No hard rubbing or anything - they basically wiped off with a few swipes. No harm to the paint either - there was not even a hint of pink/red on the white towels we were using on these two red Vipers.
Mind you, this wasn't a random test - one of our local detailers told us about this trick when we had to get a similar rash off a yellow Viper. Also good for removing those "shoe" marks on the side sills...