Collectible coins refer to numismatic items sought after for their historical, artistic, or intrinsic value. The United States 25-cent coins, commonly known as quarters, were first issued in 1796. The 1968 Denver mint-produced quarters are part of the Washington quarter series that was introduced in 1932 to commemorate George Washington's 200th birthday. Quarters minted in Denver are identified by the ā€œDā€ mint mark. Rolls of 40 quarters, or 25 cents each, are often sought after by collectors and investors for their numismatic significance and potential appreciation.