Where does “controfirma” come from?

controfirma (Italian) comes from Italian firma, from Italian firmare, from Latin firmō, from Latin Firmus, from Proto-Italic fermos, from Proto-Indo-European dʰer-mo-s, from Proto-Indo-European dʰer- — to support; to hold.

controfirma (Italian): countersignature; third-person singular present...