Sale tags show up for products that are on sale like illustrated in the image below:
Plenty of options are available to customize your sale tag and you can find them by going to Customize > Woocommerce > Product Catalog > Sale Tag.
Expand the Sale tag section to find the following options:
- Layout: simply choose if you want the sale badge to be left or right-aligned;
- Spacing: vertical and horizontal distance from the product thumbnail edges to your sale tag;
- Border Radius: use this for rounded corners;
- Badge Text: write your own label for the sale tag;
- Sale percentage: by enabling this you replace the Badge text with the actual value of your sale. Combine {value} with whatever text you want.