Collectible coins encompass a variety of types, including Proof Sets, which are specially minted coins characterized by their high-quality finish and sharp details. The United States Mint produces these sets, with the 2021 Proof Set being notable for including coins minted in San Francisco. The 25-cent coin, also known as the quarter, often features various designs that commemorate historical events or themes, making it popular among collectors. Proof coins are typically packaged in protective cases and are sought after for their aesthetic appeal and limited mintage.