All skins have a single basic rarity, which will never be changed. After initial pre-voting, skins acquire an additional rarity, defined by tier.
Skins can get into a higher rarity tier if those acquire a number of likes in pre-voting. Skins from common Loot boxes will get into Tier 0, so it won’t be shown on an NFT card.
Common, Rare, Legendary
If skin got voted for and appears in a higher tier, you will see a letter and a number in the top right corner of the NFT card, which will determine its additional rarity and tier.