This is an observation but it probaby means something.

[Jyuubislayer]

I just think this is interesting.
On the so6p's back there are 10 symbols. There are nine tomoes and one rinnegan.

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I think it is interesting also that if you take three tomoes for each sharingan transformation (or points/ "apendages" for Sasuke (his star-like mangekyo), Madara, etc.) And three for each gives us nine.
Sharingan (has tomoes) can control the first 9 tailed beasts so is rinnegan used to control the Jubi? Not really a theory, I'd just like to talk about the correlation.

 

[Prince Charles]

i think it was representing the juubi's eye.

 

[Jyuubislayer]

i think it was representing the juubi's eye.

Yeah, me too. But I think the rinnegan represents the unity of all the tomoes into one eye like all the bastsinto one being.

 

[Thane]

Many have suspected that the Rinnegan is the good side of the Ten Tail's eyes, while the Sharingan has inherited the evil side and its darker powers.

I do not believe one will be able to tame the Ten Tails, but if anyone could, it would be Tobi, with both the good and the evil eyes.

 

[Champ]

The tomoe have been thruout Naruto for the longest