The tattoo on the main character's knee in "Eastern Promises" is an eight-pointed star. This was one of many tattoo motifs traditionally used by the Russian mafia.
The production notes for the movie "Eastern Promises" describe the significance of these star tattoos. They are intended to show that the character is a high-ranking member of the Russian mafia. The placement of these tattoos, on his knees, is symbolic of the fact that he does not need to kneel to anyone, since he is of such high rank. Another meaning commonly ascribed to these tattoos is a refusal to kneel before the authorities.