10 Therefore, whosoever suffered himself to be led away by the Lamanites was called under that head, and there was a mark set upon him. ...
13 Now we will return again to the Amlicites, for they also had a mark set upon them; yea, they set the mark upon themselves, yea, even a mark of red upon their foreheads.
14 Thus the word of God is fulfilled, for these are the words which he said to Nephi: Behold, the Lamanites have I cursed, and I will set a mark on them that they and their seed may be separated from thee and thy seed, from this time henceforth and forever, except they repent of their wickedness and turn to me that I may have mercy upon them.
15 And again: I will set a mark upon him that mingleth his seed with thy brethren, that they may be cursed also.
16 And again: I will set a mark upon him that fighteth against thee and thy seed. (Alma 3)
We can read about this curse in the writings of Nephi:
20 Wherefore, the word of the Lord was fulfilled which he spake unto me, saying that: Inasmuch as they will not hearken unto thy words they shall be cut off from the presence of the Lord. And behold, they were cut off from his presence.
21 And he had caused the cursing to come upon them, yea, even a sore cursing, because of their iniquity. For behold, they had hardened their hearts against him, that they had become like unto a flint; wherefore, as they were white, and exceedingly fair and delightsome, that they might not be enticing unto my people the Lord God did cause a skin of blackness to come upon them.
22 And thus saith the Lord God: I will cause that they shall be loathsome unto thy people, save they shall repent of their iniquities.
23 And cursed shall be the seed of him that mixeth with their seed; for they shall be cursed even with the same cursing. And the Lord spake it, and it was done. (2 Nephi 5)
This is something Joseph Smith would have needed to remember for quite some time without any notes, probably more than six weeks based on our best understanding of the order and pace of the translation.