Meaning: Symbolic of Blood, Guilt, Sin
Isaiah 1:18
Come now, and let us reason together, saith the Lord: though your sins be as scarlet, they shall be as white as snow; though they be red like crimson, they shall be as wool.
Rev. 17:4
And the woman was arrayed in purple and scarlet colour, and decked with gold and precious stones and pearls, having a golden cup in her hand full of abominations and filthiness of her fornication:
"Most of the spectators testified to having seen, on the breast of the unhappy minister, a SCARLET LETTER the very semblance of that worn by Hester Prynne imprinted in the flesh."
Nathaniel Hawthorne, The Scarlet Letter (1850)