For as long as I can remember, we have heard about the CC mint Mark next to the cheek or under the chin. I have three of one, five of the other and showed them to my wife, Linda, asking her if she could see the difference. Being much smarter than I, she said: "Sure, one has a comma after Cemtral City and before Colorado on the rim, the other doesn't."
So much for me expertise. Seeing the comma is a little easier than trying to measure 1/8 of an inch.