checkbox does nothing

Hi, I put a checkbox into my form and I can see it but when I check it off, I don’t get any indication in the message that it was checked off. Should there be a checkmark or x or a yes or no or something in my message? How can I fix this? The box was to check off “I would like to receive your newsletter.”

http://ww.wp.xz.cn/plugins/contact-form-7/