To sign off on a Christmas card, you can simply add your name or a personal message. For example, you could write "With love" or "Best wishes" followed by your name. Alternatively, you could write a short message about the occasion or the recipient, such as "Merry Christmas and Happy New Year" or "May this holiday season be filled with joy and love." The important thing is to make the message personal and meaningful, so that the recipient feels appreciated and valued.