obsign
To seal; to confirm, as by a seal or stamp.
obsolete
He willeth us to eat of the bread […] and drink of that cup all, […] that is, take it as the sacrament of his body and blood […] whereby he doth represent, and to our faith give and obsign unto us, himself wholly, with all the merits and glory of his body and blood.
a. 1555, John Bradford, letter to Master Richard Hopkins
Where it comes from
Borrowed from Latin obsignō. Doublet of obsignate.
Adapted from the Wiktionary entry obsign (CC BY-SA 4.0).