Saw some posts about identifying sale items on your online store.   I have made a template in Photoshop.   In the file are 6 different Sale banners that you can place on top of your item graphic.  You can edit them any way you want.  You can also use this template to create the square image of your item that is needed to display in Square.

For those of you who don't have Photoshop, you can use it in Gimp, a free graphics program. (Free Download).