On the rear sight, it's not the elevation or the ladder that you have pictured, that looks fine. It's the wings that form the base of the site. You would see a 1,2,3,4 on it for yardage on the side. To my eye, the very top of it has been filed flat. You might not be able to see the numbers through the plating.
I've never heard of plating done by the military for use at sea. Maye , just not familiar with it. Usually, from what I've seen, when they are plated it could have been done by a veterans organization and the firearm used as a ceremonial/parade prop. It's just part of its history.