I find these mint marks frequently and have assumed they are a result of Machine Doubling. I have never found a real RPM that I know of, so I may post a few finds here if you all don't mind helping with identification?
Definitely machine doubled. But if you look further there is also DDD on the date. You won't find an RPM on a coin minted after 1989. The MM was added to the design and no longer hand punched into the dies.
The first thing you could do is research which coins have an RPM. Then you would have a list of which year/mint mark to check for an RPM and, if you kept those references you would then have good pictures to compare. edit: Such as: https://doubleddie.com/307764.html http://varietyvista.com/CONECA Master Listings.htm
Thanks everyone, I will keep hunting, I feel better knowing this is machine doubling even though it is post 1989. If I find this on pre 1989, I will recognize it. I was just using it as an example. I will try to remember the cutoff date for the rpm.
Here is another example of a post 1989 mint mark issue. I clearly see what looks like another letter under the mint mark. so what do you all think ?
Lets just start by saying that just because the coin is pre 89 clad and nickel is very susceptible to having MM that are worthlessly doubled knowing what you are looking at would be a better outlook. Study what true RPM's look like. Look around the rest of the coin and find out if there are other features that look like the MM. If this is so then it is not an RPM.
