Cleaning burned rubber from exhaust chrome?

[Phil]

Howdy,
I am new to this forum and also new to motorcycling. Got my GZ250 about 2 weeks ago and have around 300 miles on
it so far - that gives me a grand total of 300 miles of lifetime motorcycling experience, not very much!

Being older than most riders some things aren't as easy for me as they seem. For example, while I thought I was,
apparently I don't seem to raise my leg quite high and wide enough as I mount and dismount the bike and this has caused
the rubber sole of my boot to very slightly graze against the hot exhaust. It has left these ugly looking black burned on
rubber marks on the chrome exhaust and I can't seem to get them off. I have only tried rubbing them off and Honda
spray cleaner -- been afraid to try anything more exotic. Does anyone have any suggestions on what I
should use?

Thanks,

Phil