Some of them are placed where your eye just skips past. And it is an understated, subtle mark anyway, easily missed
The other thing you see is the monogram of Gilroy Roberts, who designed the reverses. It should be the same monogram he used on the Kennedy half.
I'm not sure where you're getting this from. These aren't 17th century hammer-struck siege coinage where the graders are unfamiliar with them. These are generic modern proofs. There is zero learning curve needed to grade these. And not to burst your bubble on the grades, but the Franklin Mint produced extremely high quality coins. The average grade of the ones sealed in plastic is probably 68+.
In reference to the Franklin Mint. I think the mint itself no longer functions. They still have a website. As to there prodcuts: https://billhicksisdead.blogspot.com/2012/04/sucker-born-every-minute-franklin-mint.html
Here is an article on the Franklin Mint. It is a bit of a surprise to me that the Franklin Mint origins of these coins might be of more importance than the national endorsment of the coin as legal tender - https://coinweek.com/education/the-rise-and-fall-of-the-franklin-mint/
This story gets told again every so often in the coin media. IMO it serves as a sort of warning to those that might abuse the collector market (ie US Mint) - be careful of killing the goose that laid the golden egg. That having been said, they (the FM) did make some wondrous coins of exceeding beauty and also some very rare currency issues struck in very ordinary metals such as copper copper-nickel, etc. And a number of these actually and contrary to many opinions proferred reached circulation channels. The precious metal versions did not to the best of my knowledge.