Fear of missing out (FOMO) can be a strong driving point to inspire action in an individual. Showing a visitor to your site that they’re missing out on something that everyone else is buying into is an effective way to get them to buy in. Adding a deadline to the sign-up or purchase process is an additional consequence that people will want to avoid by acting. Use tools like Ryan Kulp's Fomo to set up a quick and easy social proof prompt.