I have shirt pattern sheet that says to make a t-shirt with cut outs in it:
Make a heart or other design and put it on inside of a t-shirt. (The inside of where you will want the fabric to show through.)
Take a ruler and mark in 1" squares. Sew on these squares and clip diagonally both ways and you will have a beautiful shirt with the under fabric showing through and since it is usually knit or sweatshirt fleece it will not ravel.
To make it interesting, try different shapes. Make sure the back fabric is sewn in the shape desired before marking into 1" squares. Enjoy