How can I prevent people from sharing proofing events?

If you do not want your customers to easily share their proofing events through social media you can turn off sharing. 

Open the event from the proofing control panel and click on the gear (top right corner). 

Toward the bottom of the page there is a section for Allow Sharing. Select No, and save changes.

Now the share icon will not appear from the large view of images, or from the menu bar.