I usually just do not sign without saying anything and have not had a problem returning doctors forms mostly empty (especially no SSN, that's asking for trouble

I usually just do not sign without saying anything and have not had a problem returning doctors forms mostly empty (especially no SSN, that's asking for trouble). It's highly likely that no one at the office has any more insight into why the information is being asked than you do. If it's critical they won't leave it to a line on one of many forms.