Maybe this would work to get it off?
http://www.i4detailing.co.uk/acatalog/Autoglym_Intensive_Tar_Remover_1.html
If it is tar , which it does look like then the AG intensive tar remover will shift it no problem .
do look like shoes scuffs to me mate, the rubber might be the best bet, failing that have you tried light presure with your finger nail?