It is die wear. All the devices that face the rim are affected this way. As the die ages it starts die flow to the rim and it isn't pretty as the die ages.

https://www.coincommunity.com/forum...EAR_CENT.jpg
https://www.coincommunity.com/forum...n_PAGE_1.jpg
https://www.coincommunity.com/forum...n_PAGE_2.jpg

https://www.coincommunity.com/forum...EAR_CENT.jpg
https://www.coincommunity.com/forum...n_PAGE_1.jpg
https://www.coincommunity.com/forum...n_PAGE_2.jpg



























