Felt dots are a simple circle of felt with an adhesive backing.

Felt dots are commonly adhered to the back of items such as picture frames to stop the frame from indenting or marking the wall. For this reason, framers sometimes call them, Bump-Ons, or Wall Protectors

Felt dots commonly come in black, white or green and have a self adhesive sticker on the back. Another similar product is a felt pad which is a larger flat piece of fine thin felt commonly used to cover the entire underside of an item. 

Adhesive Felt Dots can be purchased from any craft supplies store, or framing supplies store.