Scores of these unusual coins have appeared on the market over the past decade. They are not official U.S. patterns because they were made by an outside firm -- General Motors. However, they definitely reflect an experiment in the way coins are struck and, had the experiment been successful, they might be much more popular (and valuable) today.
Perhaps the best explanation of these coins was given by Tom Delorey, noted numismatic researcher, who wrote here:
"A famous 'nonsense design' modern pattern is the General Motors roller press trial piece, coined by the tens of thousands at the GM Tech Center in Warren, Michigan where GM was trying to engineer a revolutionary new coin press for the U.S. Mint that employed a reported 144 coin dies in two opposing rollers that punched blanks out of a metal strip and struck them into coins in one continuous motion. The dies used for the testing model, which was ultimately deemed a failure when it was realized that a single broken die would force the stoppage of the entire 72-pair array, were prepared by the U.S. Mint using a female head that vaguely duplicated the relief of Lincoln's head and a wreath that vaguely imitated that of the pre-1959 'wheatback' cent, with gibberish lettering that simulated the inscriptions of same."
"Because the design did not include a denomination, security was lax and many pieces left the Tech Center as novelties. Today they are usually collected by die variety, based on letters and numbers mechanically etched into the faces of the dies in a last-ditch effort to isolate and identify the product of each die pair after striking, so that defective strikes could be destroyed if one die failed without having to shut down the entire press."
Regarding the numbers and letters that were etched into the dies, the number usually appears in the left obverse field, and the letter usually appears in the right field. However, this is sometimes switched and, in rare instances, the number appears backwards on the coin. We've seen the letters R, L, and M. If, as believed, they stand for Right, Left, and Middle, then the arrays referred to by Delorey would have contained 72 obverse dies arranged in a 3x24 pattern. Thus, in theory at least, there are 72 different combinations of numbers and letters on the obverses. We know of two different examples of the 5-L combination, so clearly duplicates exist and more may be discovered over time. None of the reverses were individually identified.