Tattoo is probably a mark by their “owner “? Is there more from the other girl?
The stars on the shoulder are a reference to the criminal world in Russia. It means to have the authority/respect in your (criminal) field, be active against the penitentiary rules, have high achievements (in criminal world).
there is also a version on the knees which means that you will never kneel before the law enforcement / public authorities.
So these two have literally nothing to do with the actual meaning of tattoos. Just for fun/fashion.
But if the guy does the same, he might have serious problems... =)