Seals - Links and a Condensed Version

http://www.disruptorbeam.com/blog/entry/a-guide-to-using-the-item-enhancement-system

Condensed version....

Seals can improve stats on weapons, armor, companions and Sworn Swords

Seals can be obtained through PtP actions, as rewards and sometimes can be bought in the shop

Seals applied to an item are permanently linked to that item

Renaming an item makes it permanent and not usable in crafting

Unlocking a seal slot with gold makes the item permanent and not usable in crafting

After reincarnation, you will need to reach level 4 before seeing your permanent Sworn Sword(s)

A permanent Sworn Sword keeps its stats/experience level and permanent gear when the player reincarnates. The gear is unequipped upon reincarnation and will be in the player’s inventory.

A seal can be replaced by another seal, the original seal will be lost