There has been nothing posted in this thread that makes me think the marks are hardness test. I don't feel it's possible to know for sure.
So I dont have the 30 years of experience and maybe some one else will chime in with exp in Rockwell Tests. Also I dont have thw coin in hand. But in my opinion, the 90 D looks like a plating blister. And the reason I say that is there ia another one right above it with the black stain around it. Also, the dot is not symmetrical. Starting in 1982 the mint changed the composition of Lincoln cents from copper.zinc alloy to a copper plated zinc Planchet. There has been problems with the copper plating ever since. Sometimes it is fine, and other times there are one or two bubbles of air and sometimes there are numerous gas bubbles of all different shapes. Finally as I breifli mentioned before, the mint has stated that the testing of the die that strikes the coin is not on the face of the die but is on the "neck" of the die. So the indentation on the die face necessary to leave a raised dot on the coin's obverse or reverse would not be made by the mint and then put into service striking coins. The working life of a die is tens of thousands of strikes, which would leave a dot in the same place on tens of thousands of coins. This is my less than professional opinion and if you can find some references or sources that tell me I am wrong I will admit it and defer to that expert. Good luck!
In the last photos it appears to be done by a drill bit as the spherical ball of a hardness tester under pressure would produce an ultra smooth surface. Also there would be no way to penetrate as shown by the small opening at the base of the 'drill pit" as the bottom of the sphere could not penetrate it. Just "someone " producing a fake. IMO, Jim
@Kein When you mention the coins that weren't supposed to be, but are, I can begin to understand your point, however, how do you know , or better yet , how can you prove that these coins are what you say they are? That's really the bottom line, isn't it? Regardless of what anyone here, including myself, says about the coins.
What if I were to tell you people that we have a friend of the family and this friend has a friend who is very close with the Denver mint and those 2 coins were a birthday gift that i recieved from one of them 12 years ago...any more questions???
These people are geniuses,,, this was for all you new people coming on this site and asking these geniuses if you possess a rare error coin,,, this was proof of how much these people know
