Not to be confused with sync marks. Cinch marks are small vertical scratches on a roll of film that are caused when the end of the film is pulled to tighten the roll, causing any dust on the film to make a small scratch. Too much drag on the supply while rewinding is one common way that cinching can occur.
Glossary of Film Terms - http://homepage.newschool.edu/~schlemoj/film_courses/glossary_of_film_terms/
reprinted with permission