Note: the 3 pieces of code you need to customize are in bold below:
  1. Exact name of the Unique Id that you assign to your custom component
  2. Exact name of your Model
  3. Exact name of your custom Signature field

var params = arguments[0],
   $ = skuid.$;
// get signature canvas and reset
var sig = $("#idSign");
sig.jSignature("reset");
// get signature field, set to null and save model
var model = skuid.model.getModel('Contact');
var row = model.getFirstRow();
var sigField = 'Signature__c';
model.updateRow(row,sigField,null);