I apologize for not saying Welcome! Didn't notice the post count you have there when I first commented so Welcome. Glad you asked the question.
I think that the nickel was dented at the rim before plating.
The others in the frame I would bet are mostly polished. There were sets called "Type Coins of the 20th Century" and the like that were marketed by various marketing companies and they would shine up all the coins and put them in a frame for display and sell them like that. By now, even polished coins could be toned in those frames.
It was popular in the 70's. My Dad had several of these in his office.
The silver coins are usually well worn circulated coins in Fine condition or even lower and the companies knew a way to sell these common date coins and make money.
War Nickels were available in bulk as chrome plated or "reconditioned" they would call it, and they were sold cheap.
Chances are the same people who put together these frames, bought quantities of plated
War Nickels to use rather than polish them up themselves.
I bet you have a "Steel" cent from 1943 that appear to look just like this nickel does. They plated a lot of steel cents too.
Edited by TNG
06/12/2017 12:39 am