"It is a Blood Quill," Harry revealed, remembering the scorching pain from when Dolores Umbridge had made him use such a quill as a child. That reminded him ... he still hadn’t killed her yet. That was something to put on his To-Do List. "A signature in blood is the only way to guarantee that your husband will know this is from you ... and also about how serious your predicament is. I think that should be enough to ensure his discretion. Now write."