Copper cans are very prone to water spots and oxidation, which can cause a patina to form on them like a penny (or turn them green, like the Statue of Liberty).

Copper‐Catalyzed Trifluoromethylation of Internal Olefinic C H Bonds: Efficient Routes to Trifluoromethylated Tetrasubstituted Olefins and N‐Heterocycles. Chemistry – A European Journal 2014 , 20 (12) ...

The story of the iconic American penny loafer is, like plenty of great origin tales, a bit murky, but is generally thought to have started out in the picture-perfect Norwegian village of Aurland.