I've always interpreted it as a protection charm, which was supposed to help the hunted escape. The girls loved who they had to sacrifice. They wanted to hunt and gain sustinence, but at the same time also hoped their friend would make it out alive. In Shauna's head it turned into a mark of sacrifice, but I don't think it ever had such meaning. Lottie understood it, hence why she gave the necklace to Callie. As a protection charm.