1957 D Jefferson Nickel Line Above The Mint Mark?

I've posted a similar coin in the past. This coin is VLDS (Very Late Die State), notice the frostiness. I've seen many coins with this "line" near the mint mark. These coins have been struck by a die that most likely suffered clashes that have been polished off, as you can see on the reverse the shape of Jefferson. All signs of doubling will also be the result of die cleaning/polishing.

Looks like there are a couple of shallow valleys on the reverse below the Monticello. Is that from over polishing? One of them is more prominent, from beside the M down to the bottom of F.

The "valleys" there might be PIDT, Progressive Indirect Die Transfer. It's a form of Die Deterioration that transfers the design outlines, usually the large centrally-located design elements, from one die to another. Although it more typically occurs on thinner planchets, the area you are referring to with the valleys is likely Jefferson's bust.

You can read more about PIDT here: http://www.error-ref.com/?s=pidt.

PIDT is a form of Die Deterioration that happens gradually or, as the name implies, progressively. What's happening there is that design of one face is gradually being transferred to the opposite die's face. And because it's happening with the larger design elements, that's why we'll see a "ghosted" or outlined image of Lincoln's bust upside down on the reverse face, for example.

When two dies come together when there's no planchet in the chamber, that's called a die clash. It's different from PIDT in that the transfer of images is immediate. Until that's remedied by repairing (abrading) the dies, all subsequent coins will exhibit the clash.

When a coin is struck on the obverse and flips over and is struck again, it's called a flipover double strike. They're very rare.

Looks like Ghosting to me.

Yes Profiler, Progressive Indirect Design Transfer, Internal Metal Displacement Phenomenon, aka Ghosting. It is caused by repeated strikes transferring design through the coin to the opposing die. It was common on earlier date Jeffersons and a few other denominations. Here is one manifesting itself on the obverse and reverse that is quite uncommon as it is of a more recent date.

So PIDT can occur on the Obverse also.!

I guess that it is considered an error? However, a common one?

I have a coin which may contain PIDT - maybe I will post in a new thread to see if that is correct.

Does it need to match up to where the image shows to be on an overlay?

Glad ya'll like it, yes they are errors. Nickels of recent vintage are not common. Older nickels like the OP's, pennies, dimes, and a few others are. They are better when on both sides, but often on one. I have a cent you can see Lincoln's outline very well on the reverse. An overlay is very helpful in identifying them.