Hello and 
EPNS stands for Electro-Plated Nickel Silver, which was an alloy frequently used to manufacture cutlery and kitchenware such as soup tureens, gravy boats, etc. in the first half of the 20th century. I imagine that a cutlery manufacturer was trying out his new stamp on a penny to see if it worked!

EPNS stands for Electro-Plated Nickel Silver, which was an alloy frequently used to manufacture cutlery and kitchenware such as soup tureens, gravy boats, etc. in the first half of the 20th century. I imagine that a cutlery manufacturer was trying out his new stamp on a penny to see if it worked!