"Wouldn't that have anything to do with Franky and Brook joining in the manga before the anime?
They know they're going to join anyway, so they make merchandise ahead of time."
I'm not saying that the coins necessarily mean anything, but this isn't the case actually.
Franky was a playable character in JUS with Luffy, Zoro, Nami, Robin, and Sanji even before he joined the Straw Hats officially. I remember seeing Brook on products / ads etc. before he joined even in the manga. Both Franky and Brook showed up in other One Piece products before they officially joined the crew even within the manga.
I remember with Franky in particular because there were a few Franky vs. Paulie debates still going on when JUS came out, though the cover of "Pirates vs. CP9" had pretty much solidified Franky as part of the crew well beforehand even without officially joining. Personally I had though Paulie was going to join also, but I was wrong about that. I never doubted Franky, but thought both could have ended up joining.