If not "paint" or the like, what do you believe it to be then? Do you not think it more likely that, perhaps, a bored someone did something to it as opposed to being some sort of impossible minting error? Now if you seriously do believe this some sort of error, can you reasonably explain how it both could have occurred, and why this is a more likely scenario than a post mint alteration?
It's been added to the coin, without a doubt. Whether it's nail polish, or something else, it did not leave the Mint like that. It has 'altered surfaces' on the building.
The OP coin posted about four and a half years ago? If so, there isn't a doubt in my mind that it's some sort of paint or the like, just as I said back then. You can clearly see where they went over the lines as well as places where it's been scraped off or otherwise removed. Perhaps we'll just have to disagree on this one.