She is a fan. I saw her in a online interview and shes admitted to being a deathnote fan when she was questioned about her costume she designed for one of her music videos looking a awful lot like mello. She even styles her hair like his. It was exactly his but it was the same basic design and had a lot of similarities.
The songs lyrics have a lot of similarities to his way of looking at things too. The whole stand alone complex and relying only on his family (Which is a old phrase used to describe mafia members taking care of other mafia members).
Not that Im saying that the video was made FOR or strictly ABOUT mello but she pretty much admitted that he was a lot of her inspiration for the costume and attitude. As for the L mark however, its actually stands for lamb but she may have had some inspiration from it to use that specific font.
http://www.youtube.com/watch?v=pSW0l4LeQkk