GFSignature is the class which houses some of the functionality included by the Gravity Forms Signature Add-on, it extends the GFAddOn class which is part of the add-on framework. Below are a few functions which you may find useful when working on your own custom code.
The gf_signature() function is used to return an instance of the GFSignature class.
Returns the URL for the specified signature.
$signature_url = gf_signature()->get_signature_url( $filename );
Initiates deletion of the signature file and updates the entry to remove the filename.
$result = gf_signature()->delete_signature( $entry_id, $field_id );