In Turbo 4.0 and up, you can enable a lock icon on the checkout button. If you are on a previous version of Turbo and would like to use this feature, you will need to update your theme.
Enabling the checkout button's lock icon
With the Turbo 4.0 release, you can now enable a lock icon for the checkout button which will appear on both the mini cart and the cart page. This subtle option is a great way to build trust and assure customers that your store is secure thanks to Shopify’s built-in SSL feature.
While this may seem like a small change, research and best practices indicate that the simple addition of this icon can help increase conversion rate, by reassuring shoppers that their payment and personal information is secure.
To enable the icon, head into Customize > Theme Settings > Cart > 'Show lock icon on checkout button':