LouF

I just noticed a tiny circle with what appears to be a capital "D" inscribed in the center of Lincoln's forehead on a 2008-D penny. The circle and the inscribed D are perhaps 20% smaller than the regular "D" next to the date. Thinking this might have been a design change this year, I found another 2008-D penny and no such symbol is there. I did a brief search on this forum and could not find this topic, so I apologize if it's old news, but could somebody tell me what to make of this? Thanks LF