You are avoiding the question... Ok, let's base everything on logic only without letting our respective emotions get in the way. Can you in all seriousness look at the circle on Sakura's back and then look at the one appearing on Naruto's shirt and still believe it is not the same circle? Seriously, just answer, YES or NO? Is it the exact same circle?
Please find enough humility within you to admit that the answer is YES. I mean come on, even a 3 years old child can discern shapes. Now, if you have already calmed yourself enough to feel at peace with this observation, the next logical step, as a human being with fully functional synaptic connections, is to wonder WHY: why is it the same circle?
Until now, I think we both agree that the circles are the same (I hope so, for your own sake). I hope we also agree that the knifes are the same too, not only because of their appearance, but also because of the way it is being held by both Sakura and the Reaper death seal. This is not even debatable because they really are the same. Of course, it is possible that Kishi was just drunk when he decided to draw this stuff, but in science, the most plausible explanation is considered true until a better one is found.
Next step
Answering the WHY
Here is where opinions are allowed and respect is required. Why is it the same circle and the same knife? The most Reasonable explanation I found is that a connection exists between Sakura and the So6p's familly or the bijus, therefore, the power of the tree.
You may agree or not with this particular connection, but even if you don't you still need to find a reason to explain why the circles and the knifes are the same. And coincidence is not the most logical explanation, because as I already said, a manga artist wouldn't do such a mistake.