Jaime Hernandez: The 1955 Doubled Die Lincoln cent is unquestionably the most famous doubled die coin in the entire Lincoln cent series and possibly, even the most famous doubled die coin in numismatics.
The 1955 Doubled Dies were created when the Mint struck a working hub and a working die together while they were both slightly rotated differently from one another. Consequently, this working die then received a doubled die impression and in return, it struck thousands of 1955 Doubled Die cents.
After the 1955 Doubled Dies were produced they were then mixed with millions of regular circulation strike cents from that same year. However, Mint employees caught some of the 1955 Doubled Die cents before they went into circulation. The Mint then decided that it was just not worth the trouble of melting millions of cents to retrieve the approximately 20,000 Doubled Die cents that were accidentally produced.
In the following months 1955 Doubled Die cents were finally turning up in circulation, including in cigarette packs which were being sold in vending machines. At that time, a pack of cigarettes would cost 23 cents each but the vending machines would only take a quarter and no other change. Therefore, the cigarette companies would need to place two cents inside each pack of cigarettes to be given back as change. Anyone who inserted a quarter in the vending machine would then receive a pack of cigarettes with two Lincoln cents inside a cellophane packaging. This cellophane packaging was then wrapped around the cigarette packs with the two Lincoln cents inside it, and this is where many of the 1955 Doubled Dies surfaced.
Since 1955 Doubled Dies were being found the same year in which they were released, many coins were pulled aside and preserved. Because of this, most coins exist in AU grades and higher. The original estimate of existing 1955 Doubled Die cents was anywhere from 20,000 to 24,000 coins. Nonetheless, many coins possibly got lost in circulation and the amount of surviving examples may be more like 10,000 to 15,000 examples in existence in all grades combined.
In conclusion, due to the high prices that the 1955 Doubled Die Lincoln cents command, there are many deceiving counterfeit coins out there in the market. One of the main diagnostics of a genuine 1955 Doubled Die cent can be seen on the reverse of the coin. Since there was only one pair of dies used to create the 1955 Doubled Dies, all genuine examples should display vertical die polishing lines to the left of the letter T in ONE CENT. Authentication is strongly recommended for this variety.
Ron Guth: In November 2010, John Wexler reported a 1955 Doubled Die Cent discovered by Richard Snow with curious abrasions on the obverse and reverse, indicating that operators at the mint may have removed the dies from the press to grind off clash marks. Two incredible scenarios arise: either the press operator missed the doubling of the dies during the abrasion process OR the press operator noticed the doubling and replaced them into the press anyway! The authenticity of the abraded die 1955 Doubled Die Cents has been confirmed by the presence of diagnostic vertical die scratches coming down from the left bar of the T in CENT.
Sources and/or recommended reading:
"1955 Doubled Die Obverse Cent Story Gets Even Stranger" by John Wexler, COIN WORLD, November 22, 2010, pp. 5, 58 and 60