In “Lucky Penny,” the penny Ted finds is stamped with the year 1939. He discovers it on the subway and assumes it may be valuable, but selling it to a collector brings him only $1.50.
That small discovery triggers the episode’s elaborate chain of cause and effect. Ted and Robin spend the money on hot dogs, which leads them to encounter Lily outside a wedding-dress sale. Their later delays, combined with a subway incident involving Barney and Ted’s court date, cause Ted to miss a flight to a job interview in Chicago.
The episode aired on February 12, 2007, as season 2’s 15th episode. Its title refers both to the coin and to the idea that apparent bad luck may ultimately be beneficial. Ted loses the Chicago opportunity, but staying in New York preserves the path toward meeting his future wife. The penny is therefore more important as a plot trigger than as a genuinely valuable collectible.