The white shield that was the mark of noviceknights, especially in Arthurian legend. (http://www.dictionaryfocus.com/?action=definition&word=vergescu)
"Quentin felt like the little boy at the beginning of The Lorax, at the mysterious tower of the dismal Once-ler. They should have been facing down bellowed challenges from black knights bearing the vergescu, or solving thorny theological dilemmas posed by holy hermits. Or at the very least resisting the diabolical temptations of ravishing succubi. Not fighting off seasonal affective disorder."
- Lev Grossman, The Magician King