Well, if your story takes place after Jesus, you could still use the cross.
Also, some theologians have argued that Jesus dying on the cross was an act of salvation for all humanity, past and present. So the symbol of the cross could arguably have godly significance even if mere mortals hadn't yet lived long enough to find out why.
If your story takes place prior to Jesus' birth, you could still go with Jewish holy symbols.
You could have one of your characters be able to write out the "logos" the word of God, and use that as a way of trying to impose obedience upon the unruly Lilith.
I'd really check out some books on Jewish folklore and the kaballah for more ideas.