Iowa Code § 814.14: Certificate of release.

When an appeal is taken by the defendant and the defendant is released, the clerk of the district court must give to the defendant or the defendant’s attorney a certificate, under the seal of the court, that an appeal has been taken and the defendant released. The sheriff or other officer having the defendant in custody must, upon receipt of this certificate, discharge the defendant from custody and return to the clerk of court who issued it the execution under which the sheriff or other officer acted with the sheriff’s or officer’s return thereon.