Again, just enough energy for one post today. It is a Missouri State Seal button, worn by various state officials and state-police officers. Your button shows the seal on a smooth (not lined) background, and the knight's helmet has three face-bars, so it is button MO-3-B in the button-book by Alphaeus H. Albert. Yours has the late-1800s-through-mid-1900s version of "Superior Quality" backmark.