Probably struck through grease which obliterated most if not all of the last digit. I am probably wrong but I see a ghost "2" where the 4th digit is supposed to be and considering that "LIBERTY" is weak on the coin, you might have a 1922-"No D" Lincoln Cent. Now, you just have to use a microscope or something to enhance the area where the 4th digit is or should be to see if it is in fact a "2". If it is, then you likely have a $500+ coin.
Frank