It was once called the Illinois Traction System. In 1937 it became Illinois Terminal System. Sold out in 1982. Going by the chart below, the "L" makes it 1949 or 1969.

The USPC coding system began in 1904 and applies only to the Ace of Spades at the time of manufacture. It also applies only where there is a letter followed by 4 numbers. Chart is below.
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(Wikipedia: http://en.wikipedia.org/wiki/Illinois_Terminal_Railroad)

Robert
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James Cagney and Humphrey Bogart in "The Oklahoma Kid" (1939). This lobby card (not mine) went for $311 at auction in February 2010.