Importing signatures into Petition?
So I figured out how to do this, for the future.

You need to import an Activity for each contact. Match as per any other import

Key import details:


source_record_id = petition id (you may have to look into the db to find this)
activity type = 32 (or the activity type id listed for Petition Signature in Administer > Customize Data and Screens > Activity Types)
subject = by default, this is the title of petition
data = date signed