@Urouge:
How does having different clothing remove a tattoo? Her arm was also clearly visible in chapter 666 in two panels with no hint of a tattoo.
I guess I don't understand the logic of needing to cover it up.
I remember some folks saying things like "in the next panel, the tattoo is gone." I am saying well her clothes are different so some amount of time has passed.
As I said above, if it is a tattoo, I could see Monet covering it up possibly because of Law's arrival. Why? I don't know, but they did have the same boss at one point, though seemingly not at the same time.
Around the time Mocha and the others met Caesar his goons were still in balloons. So pre Law there is a glimpse of a tatoo. But with that said it would have to be assumed that when Monet is giving the candy it was after Law arrived on the island, which doesn't make too much sense if her memory is chronological, unless its just any random time she is giving candy.
What ever it is it certainly isn't hair from any character. Could be a mistake, but I think it's something to just keep an eye on.