To cover the back of; to load or burden.

To write one’s name, alone or with other words, upon
the back of (a paper), for the purpose of transferring it, or to secure
the payment of a /ote, draft, or the like; to guarantee the payment,
fulfillment, performance, or validity of, or to certify something upon
the back of (a check, draft, writ, warrant of arrest, etc.).

To give one’s name or support to; to sanction; to aid
by approval; to approve; as, to indorse an opinion.