Julia Casey writes:

Mabel Green's Locket

Gift from Colonel Edward H. R. Green to his wife

United States Air Post 1918 24c Carmine Red and Blue, Center Inverted (C3a), position 9, never hinged, straight edge at top, short corner perforation at upper left, trivial corner creases at bottom left and right, encased back-to-back with never hinged example of the normal stamp (C3) in gold-rimmed glass sided locket with clasp, one side with small chip at bottom.

When Mabel Green died in Miami at age 79 in April 1950 she bequeathed the locket to her longtime companion Dorothy Nicholson. Dorothy moved to Long Island, later marrying a New York lawyer named Lester Stickles, the locket remained in a safety deposit box in New York.

As the years passed collectors began recording all the known positions from the sheet from the numbers Eugene Klein had penciled on the backs of the stamps in 1918. Only one stamp from the top row eluded the researchers; position 9. In an interesting twist position 18 from the Miller collection housed at the New Public Library was stolen in 1977 along with 53 other rare stamps. Recovered in the early 1980's its perforations had been removed at top and its number on the reverse had been altered from 18 to the missing number 9. Finally on December 26th 1984, George Amick, author of The Inverted Jenny, Money, Mystery, Mania (1986) was permitted to photograph the locket for the first time. By comparison to the adjoining stamps it was confirmed as the missing position.

To read the complete lot description, see:
United States Air Post 1918 24c Carmine Red and Blue, Center Inverted (C3a), position 9, never hinged, straight edge at top, short corne...(https://auctions.stacksbowers.com/lots/view/1-1DLCA/united-states-air-post-1918-24c-carmine-red-and-blue-center-inverted-c3a-position-9-never-hinged-straight-edge-at-top-short-corne)

Julia adds:

Two of the most fabled inverted Jenny stamps (my opinion) but not known by many collectors are the inverted Jenny locket and the used inverted Jenny. Both are associated with Colonel Green's wife, Mabel. The later stamp, she took from his desk to mail a letter to him, not realizing its value. Colonel Green went into shock when he received the letter and noticed the stamp, but took it in stride. That is NOT the one being sold.

To read the complete article, see:
US inverted Jenny locket up for auction again(https://stampbears.net/thread/3339/inverted-jenny-locket-auction-again)

To read the earlier E-Sylum article, see:
COL. GREEN AND THE INVERTED JENNYS(https://www.coinbooks.org/v26/esylum_v26n48a22.html)