What does star tattoo on knee mean?

It can mean many things, but in most cases it the Russian gangsters put them on the knees. The star on the knee mean that a person doesn't fear anybody. It is called the Vor v zakone, it means thief in law, it is a Russian crime organization and a codex. The gang members put tattoo on themselves to be recognized by other gang members. They also put stars on their shoulders, that means a person is ranked higher than those who doesn't have the tattoo's on their shoulders. But if someone put a tattoo and he didn't deserved it it can be punished for doing so.