Collectible coins include various types such as Proof Sets, which are specially minted to showcase fine detail and mirror-like surfaces. The 2020 Proof Set from the San Francisco Mint contains coinage produced for circulation, along with commemorative issues. In the United States, the quarter (25c) denomination is a popular choice among collectors, with specific designs and limited production runs enhancing their value. These coins are often sought after for both their numismatic significance and aesthetic appeal.