I made a mock band hem, inspired by a book I bought recently on overlockers (The overlocker technique manual by Julia Hincks), which has many tips on different techniques. You make a sort of seam, through an s-shape fold, and it looks like a separate band of fabric has been attached to the hem.
The first step is to make the s-shape fold. Laying the fabric with the wrong side up, make a fold so that the wrong sides join. Then, with the right side up, make a fold joining both right sides.
The fold should have three layers of fabric, with the border of the fabric remaining on the edge. This edge is sewn with the overlocker. I lifted the blade to avoid cutting too much.
Once the new fold is opened, there you are, an easy way to add some variation to hems.