Hey @mstudioil,
Are you saying you’d like to place a badge on the actual category saying that it is on sale?
One way to do that would be to place a sale notice in the category description. Depending on the theme, that would be one possibility for indicating there is a sale on that category.
Another would be to actually edit the category image so that it includes sales text.
If you don’t mind doing some custom coding, you could add in a custom field to the category, like with a checkbox that indicates that it is on sale. Then write a function that adds an extra class to the body tag on that page. You could use that class as a hook to add a banner in via CSS.
That would take a bit of work, but it’s another option. You could use Advanced Custom Fields to create the checkbox for the category. Here’s a tutorial on adding a class to the body tag to finish up the rest.
https://code.tutsplus.com/tutorials/adding-to-the-body-class-in-wordpress–cms-21077
Best