It means 'Shadowhunters: Looking Better in Black Than the Widows of our Enemies Since 1234'.
Cassandra ClareDear Alec and Magnus, How are you? Everything's just fine here. Thanks for you postcard with the picture of the Taj Mahal. It looks nice. Disregard my last few postcards. I see I overdid it. To make it up to you, I'm going to redecorate Magnus's loft for free. -Izzy
Cassandra Clare