To levy upon an instrument, the levying officer shall take the instrument into custody if it is in possession of the defendant or, if it is in possession of a third person, personally serve a copy of the writ and a notice of attachment on the third person.
If the levying officer obtains custody of the instrument, the levying officer shall, if instructed by the plaintiff, serve a copy of the writ and a notice of attachment on the obligor either personally or by mail. (CCP 488.440, 700.110)