Isobel mentions going "Dark Willow". This is a reference to the last four episodes of season 6 of Buffy the Vampire Slayer, starting with "Seeing Red" when sweet Willow went crazy with the dark magic after her love was shot.
The episode title refers to the song I Saw The Sign by Ace Of Base (1992).
Although Michael Trevino is absent, he and Paul Wesley, the director of this episode, previously starred together in The Vampire Diaries (2009) as Tyler Lockwood & Stefan Salvatore.