Add labels to featured images of your products in WooCommerce with ‘Woocommerce Product Labeling’.
Promote your products by adding custom labels.
From the products edit page you can configure it.
1.- Choose a label to show (if empty, not label is shown)
2.- Select a predefined class, or a custom class to create your own style.
3.- If you have chosen the custom class, then set this class
That’s all, now you have an amazing label in your product image !
You have more information in the documentation page.