So it could not have been placed by another coin because it would have to have been a mirrored 4 to mark it like that right? Any idea of how it could have been stained? Do you ever run across this type of thing?
Interesting, but probably coincidental as others have said. Our eyes play funny tricks on us. At first glance it does have a remarkable resemblance to a 4, but on closer inspection, the top of the vertical line seems to have more of a blotch than a sharp meeting point, the horizontal line isn't completely horizontal but tails up on the left. Just attempting to examine through slightly more critical eyes.