Collectible coins, particularly those from the United States, include various denominations and commemorative issues. The 1 cent coin, or penny, has seen several designs and types over the years. Proof sets, such as the 2020 San Francisco Proof Set, feature coins that are struck with a higher level of detail and polished surfaces, making them ideal for collectors. These sets are typically produced in limited quantities, enhancing their value and appeal in the numismatic market.