Collectible coins can include a variety of types such as circulation coins, commemorative coins, bullion coins, and medals. In the United States, modern commemorative coin sets are issued to mark significant events or anniversaries. The 2020 Philadelphia Modern Commemorative Sets showcase specific themes and celebrate American heritage, often featuring unique designs and limited mintages that appeal to collectors. These sets typically include both proof and uncirculated coins, enhancing their value and desirability.