A small percentage of 1972-D Half Dollars lack the designer's initials (FG for Frank Gasparro) on the reverse between the eagle's left leg (viewer's right) and the tail. While this appears to be a mistake on the engraver's part, it is more likely that the dies were ground down to remove clashmarks, and in the process, the initials were effaced. Similar "No Initial" Half Dollars occurred on some 1966 and many 1982-P Half Dollars. Credit for the discovery of this variety goes to Kip Nelson, who discovered it after the 1982-P No Initial Half Dollars were discovered by yours truly in 1983.
Breen called this variety "Presently very rare," which remains true today. The finest examples certified by PCGS rate only MS63.