Collectible coins refer to numismatic items sought after by collectors for their historical significance, rarity, and aesthetic appeal. The United States' Twenty Dollar Liberty Head Double Eagles, minted from 1849 to 1907, feature a depiction of Lady Liberty on the obverse and an eagle on the reverse. The 1870 issue is particularly notable, as it represents a year of limited mintage and interest among collectors, enhancing its value and desirability in the market.