Stamped on the back of each pin is the imprint "©WD". This particular Dopey comes from blog reader, Debi. "I found it in my great grandmother's Hoosier cabinet stored in her basement. Many items from 1930's were in there including this pin."
The pins do show up every so often on ebay and other online seller sites.
While the whole collection was manufactured by Brier, note that the brand name "Nemo" is only marked on some of the cards and not others. The "Nemo" (or "Little Nemo") name was used on other Brier jewelry from that era and actually comes from the "Little Nemo in Slumberland" cartoon strip which ran in the New York Herald and New York American between 1905 and 1926. NEMO INFO VIA PAST AND PRESENT JEWELRY.
Series images via Hakes.
Other Brier items are included in the 1974 book, Disneyana, by Munsey, p.136.
In an earlier Archive entry, see the 1938 Brier sweater pin featuring Snow White and Doc.