A simple solution would be to add [Coming Soon] to the product's titles, or photoshop the text on top of the product image itself.
If you would like to have this text coded in, our theme support team can assist by using the design time on your account! You can learn more about design time here.
If you would like to utilize some of your design time, we’d be happy to continue assisting you through live chat, email, or callback. Please visit our Help Center and log in to your account to create a support request.
Hope this helps!
I would recommend enabling the option for Shopify to track your inventory, and then set the inventory to 0 so it cannot be purchased.
When inventory is set to 0, most themes will display a sold out badge! To change the sold out badge to 'coming soon', head to your theme's language editor (Online store > Themes > Actions > Edit languages) and search for 'Sold out'. From there, you can change the text.
Let me know if this helps!
Thanks for letting me know!
By using your design time, our Theme Support team should be able to help add an additional badge for products that are 'Coming Soon'!
Alternatively, there are apps for pre-orders you can consider here.