Collectible coins, such as those issued by the United States of America, can encompass a range of types, including patterns. A notable example is the 1864 Philadelphia coin, which is categorized as a pattern coin and often designated as PH10c. Pattern coins are experimental pieces created to test new designs or compositions before mass production. They typically feature unique designs that differentiate them from regular issue coins and are highly sought after by collectors due to their rarity and historical significance.