From around 1516 Luther used his own seal, in which, as he said, his whole theology was summarized. Nowadays it is still a worldwide mark for the Lutheran churche. It consists of a black cross in a red heart, within a white rose, in a blue field, in a golden ring:
He describes the meaning in a letter to Lazarus Spengeler from the Coburg in 1530 (WABR 5, 444v.):
Grace and peace in Christ! Dear sir, my beloved friend! As you desire to know whether my painted seal is correctly displayed, I want to tell you as my good friend my original thoughts, which I wanted to summarize on my seal, as a symbol of my theology.
The first is a cross, a black cross; it stands in a heart, which retains its natural colour, so that I would remind myself that faith in the Crucified saves us. For one who believes from the heart will be justified. Although it is indeed a black cross, which mortifies and which should also cause pain, it leaves the heart in its natural colour, it does not corrupt nature, that is: it does not kill, but keeps alive. The just shall live by faith, but only 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. Not as the world gives peace and joy, that is why the rose should be white, and not red, for white is the colour of the spirits and the angels.
Such a rose stands in a sky-blue field, because that joy in spirit and faith is a beginning of the heavenly future joy. We are there already; we have it in hope, but it is not yet public.
And around this blue field is a golden ring, which wants to tell us that such blessedness in Heaven lasts forever and has no end, and it is so much more exquisite, beyond all earthly joy and goods, as gold is the most valuable, most precious and best metal.
In 1540 Luther’s wife Katharina von Bora added the Luther rose to the lintel above the entrance of the Augustinian Monastery, where the family of Luther lived.