# even if you ... were the signet on my right hand

Yahweh speaks to Jehoiachin as if it were possible for him to be the ring on Yahweh's hand.

# the signet on my right hand

"the signet ring on my right hand that represented my authority to be king". A signet ring was used by a king to place his seal of authority on documents. It represents authority to rule.

# I would tear you off

"I would tear you off from my hand" or "I would quickly pull you off of my hand"