Nevr Dull cotton wadding polish wipes away bootmarks like magic. Just don't rub too hard or you'll cloud your finish.

 

A pad of "0000" steel wool and a couple of minutes will have all the marks off it. The "0000" is the finest-grit steel wool and I've used it for years on chrome. Don't go any coarser than "0000".

My Fat Boy was used when I bought it and had a number of melted boot marks on the pipes. The steel wool and a couple minutes of work had all of them gone. Looked so good that I went over the rest of the exhaust too - shined it all up to brand new again.

 

I know you recommended the finest wool, but having seen someone try to remove rust with wool, and "satinized" his pipes, I'd wonder what is happening on a micro scale using ANY steel wool, considering that just wiping with rags on a dirty pipe will scratch it, bit by bit, until it's satinized. Ask me how I know.
I do know that the solvent doesn't harm the chrome. I'd rather not chance anything that can be abrasive on any level, personally.