80's movie.
When some guy gets bit by a werewolf this symbol (I'm not sure if he was bitten on the hand or what) forms on his hand. He ends up being sick in bed until he transforms at the end.
He was lived with his little sister and mom, I think.
Anyway he becomes a werewolf at the end and his family (sister and mom, or whoever they were) are running around scared of him. His friend comes over and sees him and starts laughing for some reason. I don't remember if he kills his friend or not. At the end it shows him outside howling.