Dale, I understand, and the rules confirm, how the player “SHOULD” mark his ball. But, understand…it is not MUST mark his ball. The ROG state how it should be done. So, if the guy does not mark his ball with a coin or object…instead uses the putter head…and then puts his marker at the other end of the putter head…it is NOT a penalty as long as his procedure to move his ball back to its original position is exactly the same. Decision 20-1/16 covers this quite well. In that decision, is specifically mentions using the toe of the putter. So, while I do not like to see people use this method, it is definitely legal as long as when they move it back, they do not put a coin or marker down and then put the ball ahead of it.
In Jon Rahm’s case, he marked his ball beside it (initially) instead of behind it, as the ROG state it “should” be marked. However, in moving the ball back, it looks a bit off but honestly I have to agree with the R&A ruling…it was off maybe a milimeter or so at best. The angle of the camera was not directly over the ball.