mid-15c. (implied in consigned), "to ratify or certify by a sign or seal," from French consigner (15c.) and directly from Latin consignare "to seal, register," originally "to mark with a sign," from assimilated form of com "with, together" (see con-) + signare "to sign, mark," from signum "identifying mark, sign" (see sign (n.)).
Meaning "deliver into the possession of another" is from 1520s. Specific commercial sense "to transmit to another in trust for sale or custody" is from 1650s. Related: Consignee; consignor.