The Melvin Purvis Junior G-man Corps ring was issued in 1936 as a premium of Post cereals. Hake's price guide values it at $60 in Fine condition.
FBI agent Melvin Purvis was best known for having led operations that resulted in the deaths of notorious bank robbers John Dillinger and Charles Arthur "Pretty Boy" Floyd. After Purvis's retirement from the FBI in 1935, Post featured him in massive advertising campaigns in newspapers and magazines, and of course on their own cereal boxes. (Post often preferred print media rather than the radio promotions favored by other companies who targeted kids in their marketing.) There were numerous other Purvis premiums: paper items, pens and pencils, pocketknives, fobs, whistles, and especially toy badges.