My seal is a symbol of my theology. The first should be a black cross in a heart, which retains its natural color, so that I myself would be reminded that faith in the Crucified saves us. "For one who believes from the heart will be justified" (Rom. 10:10). Although it is indeed a black cross, which mortifies and which should also cause pain, it leaves the heart in its natural color. It does not corrupt nature, that is, it does not kill but keeps alive. "The just shall live by faith" (Rom. 1:17) but by faith in the crucified. Such a heart should stand in the middle of a white rose, to show that faith gives joy, comfort, and peace. In other words, it places the believer into a white, joyous rose, for this faith does not give peace and joy like the world gives (John 14:27). That is why the rose should be white and not red, for white is the color of the spirits and the angels (cf. Matt. 28:3; John 20:12). Such a rose should stand in a sky-blue field, symbolizing that such joy in spirit and faith is a beginning of the heavenly future joy, which begins already, but is grasped in hope, not yet revealed. And around this field is a golden ring, symbolizing that such blessedness in Heaven lasts forever and has no end. Such blessedness is exquisite, beyond all joy and goods, just as gold is the most valuable, most precious and best metal. This is my compendium theologiae [summary of theology].
Though I had not previously seen the Luther Rose, a fairly common symbol of Lutheranism, the basic image struck me as oddly familiar: it looks like the Sacred Heart of Jesus (left and right). As Luther's description makes clear, the heart in his seal symbolizes the heart of the believer, not the heart of Jesus. Still, the visual similarity seems striking. I do not know when the contemporary style of depicting the Sacred Heart began; devotion to the Sacred Heart took off with the visions of St. Margaret Mary Alacoque (1647-1690), though earlier versions of the devotion can be found as early as the eleventh century, before the Reformation. Is it possible that the image of Luther's seal was inspired by the Sacred Heart, even if the meaning of the symbols was changed?
In any event, today the Catholic Church celebrates the Solemnity of the Most Sacred Heart of Jesus.