Definitions of countersignature
one person's signature next to another person's signature to confirm that the other person is who they say they are
The form specifically states that a countersignature is required.
There are multiple definitions - click on the translation that matches your context.
countersignature means:
substantiv
full
noun
one person's signature next to another person's signature to confirm that the other person is who they say they are
The form specifically states that a countersignature is required.