As a date, the 1922-D Cent is one of the most common of the 1920's, especially in terms of the number of certified examples. However, the real interest in this date comes from the fact that no Cents were produced at Philadelphia or San Francisco in 1922. Even better, this date is the "father" of the 1922 Plain (actually a 1922-D with a clogged mintmark).
Collectors must be very careful with this date because of the degrees by which the mintmark disappears on some dies. Collectors must discern between 1922-D Cents with bold mintmarks, weak mintmarks, "ghost" mintmarks, and coins that appear to have no mintmark at all. The degree to which the mintmark disappears affects the value of the coin directly. Visible mintmarks (strong or weak) carry the least premium. "Ghost" mintmarks, where the mintmark is barely visible, qualify as "Weak Mintmarks", a die variant of the 1922-D, but one which carries a nice premium. Finally, the "Plain" version is the most valuable, and the one with the strong reverse is the most desirable.