Depends if you have SC armor or got ToA its probably better then anything you can get in DF but if not save them depending on what type you have they either be sold, uncrafted<salvaged>, or buy things.
On our Role Playing sever the prices are like
1 gold = Deamon seal
5 gold = saphire
10 gold = diamond
If you craft you can get more money then what they sell/buy for but you have to salvage them to do it. Other servers will be different prices.
I believe those use to be the prices haven't hunted for seals long time.
However if your <25-30> you want to keep them if you
don't have any other way to get armor.
Takes about 30-35 seals of one kind for most objects.
Nimue-Gilez Cleric 50