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.
Rodeo cowboys, construction workers and oilfield workers can frequently be spotted with this "can outline" in the rear pocket of their jeans. The cardboard or plastic can will eventually wear a "ring" pattern on the jeans. The most frequent brand of jeans worn by a man with a Wrangler Skoal ring... Wranglers, of course!