That's a gorgeous button Androfan. Looking at the inscription, I think you're right that it is in Latin. I think I can make out the first word as "Sigilla" and the second might be "corona" - so perhaps it starts with something like "Sign of the crown". I checked the British orders of chivalry, and none of their mottoes are close to that. I did notice one thing though. The central figure in the design looks like a lady standing in a shield emblazoned with three lions; that's almost certainly Britannica. But the figure on the left holds a shield emblazoned with fleur-de-lys: France. I can't make out the shield on the right. This leads me to believe that it's the emblem of some organisation that spanned England, France and one other country. Given England vs France during the Middle Ages, i suspect such an organisation would be more recent in origin. Quality looks very fine and would probably be very legible to an expert equipped with a loupe. I'd love to know what you find out.