It's clearly "extra rank behind the first [rank]", and it's trying to say exactly the same thing as previous griffon standards.
So normally it's 1 rank + 0, 2 ranks +1, 3 ranks + 2, 4 ranks +2
Griffon Standard: 1 rank +0, 2 ranks +2, 3 ranks + 4, 4 ranks + 4
And in 6e it's
1 rank +0, 2 ranks +2, 3 ranks + 4, 4 ranks + 6
This still makes it much worse than before, as you get a max of +2 for the banner instead of +3 like we used to. So it's a War Banner which goes to zero if you get hit with first charge, but +2 if you have full rank bonuses. Honestly I'd rather the war banner if they cost the same, but instead it's double the points.
I think some people are reading it as capping out at +2 bonus for ranks, not 2 extra ranks being counted, so it goes
1 rank +0, 2 ranks +2, 3 ranks +2, 4 ranks + 2
So it's just a worse war banner. I clearly don't agree.
And I see someone saying
1 rank +0, 2 ranks +1, 3 ranks + 3, 4 ranks +3
if you are reading it as "behind the first [extra rank]", but that's just silly.