I think I know what you are talking about, what looks like a slightly sunken in bust-like shape of the reverse, that lines up with Lincoln's head on the front? I have noticed a good amount cents that have the same thing, a lot of 1946 cents also have this for some reason. I'm not really sure what causes it, but I remember in the past thinking that it was caused by over polished dies. Many of the 1946 cents have very polished dies (removing part of the date in some cases) along with this I also see the slight imprint of Lincoln's bust on the reverse. The 1922 no D cent, the most famous over polishing error also seems to have a slight imprint of Lincoln's bust on the reverse too. It isn't anything very collectible or rare as rare as I know, and probably doesn't add a premium to the value. I'm sorry if you were talking about something else and this isn't any help!