It's safe to share your certificate or information on your certificate on social media. Share options for Twitter and Facebook are available from the Share icon on the certificate card in your dashboard.
You can also email or post a link to the certificate. (If you share a link, make sure your certificate is set to public or no one will be able to view it.)
A Verisart certificate contains no personal information about the owner. The identity of the owner is represented on the certificate by a public 'Current Owner Key'. Copying this key does not give anyone access to your certificate details on the blockchain - although, even if it did, there's no way the blockchain record can be altered once it's created.
Download your certificate as a PDF to ensure you are posting the best quality certificate.