Collectible coins, specifically from the United States Mint, often include various types such as Proof Sets, which feature coins struck with high-quality finishes for collectors. The 2018 Proof Set from San Francisco includes several denominations, including the quarter (25c) and one-dollar coins. These sets are produced to highlight the artistry of American coinage and are typically sold in protective packaging to maintain their condition. Collectors seek these items for their aesthetic appeal and potential investment value.