This 1923 commemorative half dollar marks the 100th anniversary of the Monroe Doctrine, a United States policy rebuking European colonialism in the Americas. The coin, designed by Chester Beach, features on its obverse President James Monroe (left) and Secretary of State John Quincy Adams, who authored the Monroe Doctrine.

Nearly 275,000 were struck and were issued for $1 each, but they were so common that they were worth little over face value during the Great Depression of the 1930s -- many were spent. The majority are known in the grades of AU50 to about MS64, while MS65s are very scarce and pieces grading MS66 and higher are quite rare. Many are quite lustrous, but beware of surface marks on the coin's many flat surfaces.