Here is a nice BU Cent with quite a large abrasion on the reverse. This is a common area for this type of error for the Lincoln wheat cents. I think most of these are minor abrasions go unnoticed. The abrasion is caused by the feeder finger of the coin press rubbing on the face of the anvil die. A light abrasion will smooth or polish the die which can leave a shiny spot on the coin. If the pressure on the die is great enough the feeder finger can wear away the die which in turn will change the flatness of the coins field. Please post any coins you may have that show this type of error.
I have found these marks on 1943 cents as well and they denote that the coin has its original surface.
This form of die damage appears on cents from 1917 to 1945. Often paired, they are assumed to be caused by contact with a pair of reciprocating feeder/ejectors.
Oh great, now I have to look at all my wheat cents again. LOL Very cool though, always glad to learn something new