The second gift received from the secret knothole of the Radley oak tree were two pennies--"Indian-heads"--that must have seemed quite ancient to Jem and Scout. The Indian Head Penny was minted for a half-century (1859-1909) and were nearly out of circulation by the time of 1930s To Kill a Mockingbird. The two "scrubbed and polished pennies" pictured Lady Liberty with an Indian head dress on the front of the coin (thus, the origin of their nickname), and they held not only their present value but were probably also becoming more valuable since they were no longer being minted. But to Jem, they held an even greater importance. Believing that "they come from the Indians," Jem thought that the pennies provided a magical quality.
"They're real strong magic, they make you have good luck... things like life 'n' good health, 'n' passin' six-weeks tests..." (Chapter 4)
These were not coins to be spent, and Jem decided to "put 'em in my trunk."