Often times, it's really a Copenhagen ring (smokeless tobacco). It's a round can containing tobacco that, with most men who dip, is kept in the left rear pocket of his Wranglers, Rustlers or Levis jeans. Cowboys and other blue collar types can often be seen with the outline of this can in his rear jeans pocket. With time, it wears a white ring on the pocket, hence... Skoal (or Cope) ring.

When you eat dirt for the first time and leave your family to build a shack in the woods

A mark (ring) in your jeans where u keep your skoal. (chew, dip)