is this something or nothing?

i see this often , like a shiny spot the field of a coin, mostly nickels an quarters,not an indent that i tell, but usually has straight lines, an under microscope there looks to be a difference in the surface of the coin, could this be struck thru something, i didnt think so cause i thought that usually left an indent,

 

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Struck through a thin layer of grease. It wasn't deep enough to leave an indentation.