1776-1976 Bicentennial quarter is the only year to carry those letters. They're the monogram of Jack L. Ahr, who designed the famous Drummer Boy reverse.
Coins of the United States
The Justice League, also called the Justice League of America or JLA, is a fictional superhero team that appears in comic books published by DC Comics. First appearing in The Brave and the Bold #28 (February/March 1960), the Justice League originally featured Superman, Batman, Wonder Woman, Flash (Barry Allen), Green Lantern (Hal Jordan), Aquaman (Arthur Curry), and the Martian Manhunter. The team roster has been rotated throughout the years with characters such as Green Arrow, Captain Marvel, Black Canary, the Atom, Hawkman, Elongated Man, Red Tornado, Firestorm, Zatanna, Hawkgirl, Cyborg, and dozens of others. The team received its own comic book title in October 1960, when the first issue was published. It would continue to #261 in April 1987, which was the final issue. Throughout the years, various incarnations or subsections of the team have operated as Justice League America, Justice League Europe, Justice League International, Justice League Task Force, Justice League Elite, and Extreme Justice.
United States Bicentennial coinage
Coins of the United States dollar were first minted in 1792. New coins have been produced annually since then and they make up a valuable aspect of the United States currency system. Today, circulating coins exist in denominations of 1¢ (i.e. 1 cent or $0.01), 5¢, 10¢, 25¢, 50¢, and $1.00. Also minted are bullion (including gold, silver and platinum) and commemorative coins. All of these are produced by the United States Mint. The coins are then sold to Federal Reserve Banks which in turn are responsible for putting coins into circulation and withdrawing them as demanded by the country's economy.
Today four mints operate in the United States producing billions of coins each year. The main mint is the Philadelphia Mint, which produces circulating coinage, mint sets and some commemorative coins. The Denver Mint also produces circulating coinage, mint sets and commemoratives. The San Francisco Mint produces regular and silver proof coinage, and produced circulating coinage until the 1970s. The West Point Mint produces bullion coinage (including proofs). Philadelphia and Denver produce the dies used at all of the mints. The proof and mint sets are manufactured each year and contain examples of all of the year's circulating coins.
Jack L. Ahr
The United States Bicentennial coinage was a set of circulating commemorative coins, consisting of a quarter, half dollar and dollar struck by the United States Mint in 1975 and 1976. Regardless of when struck, each coin bears the double date 1776–1976 on the normal obverses for the Washington quarter, Kennedy half dollar and Eisenhower dollar. No coins dated 1975 of any of the three denominations were minted.
Given past abuses in the system, the Mint advocated against the issuance of commemorative coins starting in the 1950s. Beginning in 1971, members of Congress introduced bills to authorize coins to honor the United States Bicentennial, which would occur in 1976. The Mint, through its director, Mary Brooks, initially opposed such proposals, but later supported them, and Congress passed legislation requiring the temporary redesign of the reverse of the quarter, half dollar and dollar.