No easy way to import signatures to petition
So there is no easy way to mass import signatures to a petition.
When looking at Petitions on Campaign > Dashboard > Petitions on the right side under the more option, there should be an option to "import signatures", which should be a custom version of the Import Activities.
As a workaround, I had to manually lookup how to import it, include the required numeric fields for source_record_id and activity_id.
CiviCRM 5.15 on Wordpress