1979 Jefferson Nickel DDO?

The mintmark is showing a broken post issue on the center of that device. When the post breaks off the die, it can be a slow break away or happen all at once. When it happens all at once, then the base of the post may break away the area below the fields. Thus making the filled die area rise above the device.

This can happen on any closed device:


There is not premium for this. I consider this a die event. The die aging process allows this to happen. It was a normal die when it was created. So no premium.

When I see a subject brought up with a coin, I extend the information a bit more to help more of the subject information made known.