Found this today need some advice

[Oneil1979]

Got out for a hour today started scouting around other areas of my 1880s permission and this popped out! Not sure what it is so any ideas are appreciated. I am also looking for advice on cleaning in an attempt to get some of the dirt off? Looks pretty old to me, its hammered and slighlty off centered. I can make out a bust on the front and some lettering on the back.could be a button but is pretty heavy and thick for a button. Appreciate any feedback.