Thrice uses this alot, and we have it on our button. but alot of people don't know what it means.
According to Saint Margaret Mary's Diary, "After that I saw this divine Heart as on a throne of flames, more brilliant than the sun and as transparent as crystal.

It had Its adorable wound and was encircled with a crown of thorns,… It was surmounted by a cross…"
The flames coming from His Heart show the intensity of His Love and His burning desire to be loved in return.
Around His Heart is a crown of thorns signifying that His immense love for man had been the cause of all His suffering…
The wound in His Heart was made by the lance of Longinus and signifies that He is hurt by sin, especially mortal sin.
Above the flames is a cross showing that His Love for us was so great that He died for us and "from the very first moment of His Incarnation, that is to say, when His Heart was formed, the cross was planted in it, and from that moment on, it was filled with all the bitterness caused by the humiliations, poverty, sorrows, and contempt which His Sacred Humanity had to suffer during the course of His life in His Passion."
All of the symbols - the heart, the thorns, the wound, and the flames are reminders of His love: "See, O see how much I love you…"