Working swiftly and silently, someone cut the rope securing the leg of the display case and inched it forward. A sheet of protective glass was slid back, and four rare stamps were plucked from their display frame.

Minutes later - around 9:30 on a September morning in 1955 - a delegation of esteemed philatelists strolled down the row of display cases, looking expectantly for the star item of the collection: a block of four famous 24-cent stamps with the airplane in the center printed upside down in error. The stamp is known to collectors as the Inverted Jenny, after the nickname of the Curtiss JN-4 biplane.

But the block was gone. The Federal Bureau of Investigation interviewed the armed guards and others in the room and came up empty, unable to even name a suspect.

In the nearly 60 years since that theft, two of the stamps have been recovered, but the other two remain lost. Now, a prominent stamp dealer is offering a $100,000 reward to try to help close the case.

Donald Sundman, the president of the Mystic Stamp Company, a mail-order firm in Camden, N.Y., announced Saturday at an annual gathering of airmail stamp collectors that he was putting up $50,000 for each of the two missing Inverted Jennies.

The stolen block belonged to Ethel B. Stewart McCoy, one of the most prominent philatelists of her day. Ms. McCoy was a New Yorker and the daughter of Charles Milford Bergstresser, a journalist who with Charles Dow and Edward Jones was a founder of Dow Jones & Company. Her inherited wealth allowed her to happily indulge her collecting passions, which included airmail stamps of the world and stamps depicting palm trees, of which she had three albums full.

Her Inverted Jenny block was one of just a half-dozen surviving intact from the original sheet of 100 misprints, bought over a post office counter in 1918 by a lucky broker's clerk who quickly resold them to a prominent collector. That collector dispersed the sheet, mostly as single stamps, after numbering each one on the back in pencil.

Ms. McCoy's foursome had been a gift in 1936 from her first husband, so its sentimental value to her greatly exceeded the $15,000 she insured it for before lending it to the American Philatelic Society to exhibit at its Norfolk, Va., convention in the fall of 1955.

What happened afterward is described in detail by George Amick in his 1986 book, "The Inverted Jenny: Money, Mystery, Mania."

To read the complete article, see:
$100,000 Reward for Missing 'Jennies'(www.nytimes.com/2014/09/15/us/100000-reward-for-missing-inverted-jennies-stamps.html)