When asking your visitors for sensitive data, it's important that you encrypt communication from the visitor to your servers. The industry-standard method of encrypting this data is called SSL, or Secure Socket Layers.
If the webpage URL begins with "https:" it means it is served using SSL.
To help protect your visitors, SSL is a requirement for some TrustedSite trustmarks to display. For this reason, we recommend that all pages of your site use SSL and be served over HTTPS.
If you aren't currently using SSL, you can get it for free with Let's Encrypyt.