Looks like a Crown Livery button... It kinda appears to be British Crown, but It may be another part of Europe or it may be a "King Crown button" but someone else may know what country your crown yours is representing. It can be hard too put a date on a-lot of crown buttons without a manufactures name on the back of the button "Back-Mark" since so many have and are produced. Yours does appear too be a early 19th century! but like i said it can be hard too date some of these. You may want to research more into "Crown Buttons" and you may come up with something.