I have prepared the backs of my small paintings with a wood brace, eye hooks and hanging wire. They stand out from the wall between 1/4 - 1/2 inches, are gessoed on both sides in warm white and signed in pencil at the back. The wood brace is removable if you prefer framing, because it's attached using silicone gel. Here are some examples of the side and back of my work. The very smallest, mini paintings, are prepared as magnets.
I recently prepared hundreds of small panels in order to have a continuous stock at my disposal for daily painting. I was fortunate that a friend was able to cut these to size for me. It was a lot of work to gesso and sand all these panels and they turned out beautifully.
Working small enables the finishing of a work in a short amount of time which is great for experimenting, and it is convenient when traveling. Last year I began painting often on small pieces of mat board that I had a big stack of second hand. When I traveled to Argentina for two months at the end of 2018, I took the mat board pieces to paint on. When I got home to the States, I was inspired to upgrade to MDF (medium density fiberboard). I love the smooth feel of these panels. They're lightweight and inexpensive, but strong. The smallest ones are 2.5 x 2.5 inches, and there are 4 x 4", 6 x 6" and 4 x 5" pieces.