$('button[id="signup"]').click(function(){
    var serializedData = $('form[id="signup"]').serializeObject();

    alert(serializedData);

    $.ajax({
        type: 'POST',
        url: 'php/test.php',
        data: serializedData,
        success: function(data) {
            $("#response").html(data)('success', data);
        }
    });
});