It looks it's not working because of how forms styles the elements it hides with field rules. By changing when you add the signature functionality to the form, you can resolve this issue.

The original code adds the signature to appropriate sections here:

$.getScript('http://lf.d93.k12.id.us/forms/js/jSignature.min.js', function () {
    $('.signature').jSignature();
});

Replace that with the following code that waits for the user to make a selection (student or staff) and then applies the signature functionality. #q11 is the selector for the radio button you're using.

$('#q11 input').click(function () {
    $.getScript('http://lf.d93.k12.id.us/forms/js/jSignature.min.js', function () {
        $('.signature').find('canvas').remove();
        $('.signature').jSignature();
    });
});