Actually they stopped hand punching mint marks in 1989, so no RPMs should have been since then. Probably damage . Jim
I'm not Sal but this is from the US Mint: As stated above by @desertgem, after 1989 mint marks were no longer hand punched into each individual die.
Sorry, I don't see any doubling but IMO you have a filled mint mark. Filled mint marks are fairly common and add no value to a coin.
The wonders of technology. @thomas mozzillo gave you the two answers to your first question and I agree on the nickel.
Could the lettering and the face of the coins on the obverse and the reverse of these coins be due to anything other than PMD or or machine doubling
PMD and die deterioration doubling on obverse. Notice how close the lettering is to the rim, some even touch. The die spread due to over use. The reverse may have already been replace by the time of the strike. Jim
If you would point out where you see the doubling it would make it easier for us to determine what you have.
Can you look at this penny I think there is doubling on the date and In the word liberty and there I misalignment on the edge and a determination of the grade