Ususally a motorcycle with a sport oriented nature that has had most of its fairings removed to create sort of an unfinished, tough and urban look. A Ducati Monster is a prime exaple.
Look for a non-existent windscreen, loud exhast and distinct lack of platic. Dual headlights are becoming a popular option as well.
See that squid jam through traffic on the Duc? Dumbass is only wearing a half-lid so he'd better not dump it.