How do they determine the stars?

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Every member here at mylot have a star above their names...and the stars contain a number within them. How is it that someone has the number 5 and someone else has it 9 or 10? What is the meaning of these symbols? What difference does it denote and does it affect the earning? I am having the red star number 9 right now, i have passed through the previous stars quite fast but now i am stuck up at 9 for quite some time. Can anybody enlighten me on this?