You should include clear instructions on how to unsubscribe from the campaign you’re sending. For example, a request to reply with an “unsubscribe” message or a link to a page where you can register the petition.
It’s also a good practice to keep your mailing lists clean, even if they do not ask you to unsubscribe, by checking for bounces or emails that no longer exist. All of those cleanups will improve your deliverability and reduce the probability that your emails are classified as spam.
It’s a best practice, and even mandatory in some countries, to always provide a way to unsubscribe from the emails you send to others.