That article is hilarious. “It's also called a mint mark…” He did mean “on” the coin. The KM number is found on the obverse or reverse!!
"The KM number stands for Krause-Mishler Catalog Number, a system coin collectors use to classify coins based on their characteristics. The catalog numbers were assigned by John F. Mishler and Charles Krahl at Random House Books in 1970 as part of their Encyclopedia of United States Silver Coins book series (the “Red Book”)."
I'd say it's a good thing “Numista” doesn't show up anywhere in those pictures.
Coins in circulation for years can also have a ton of dirt on them—even if they’ve never been used to buy something! If you don’t wash them off before handling them, bacteria from your hands can build up on your collection over time, making it less valuable as a collector’s item (and more likely to give someone else cooties).
Errors are intentional or unintentional, but they usually occur on both sides of a coin. This means that one side will look like it should, but the other will have some errors.
The first thing you need to do is to gather your coins. Make sure to bring them in a bag or envelope, not loose in your pockets. And please avoid using glass jars or metal containers to transport them. Don’t bring them in plastic as it’s unsuitable for the coins, and they might get damaged if they’re jostled around too much during transport.
