The coin clearly has a pleasing composition, and is not complicated for copying. The top character "Ta" means great. It is a pictogram of a man with arms outstretched, saying "It was THIS big." Bottom character "Ting" is 'cheng' (order) beneath 'mien' (a roof). Thus order in the house, peace, and by extension, fixed, certain, decided. It was popular for charms.
Chinese etymology is writ more or less clearly for many words, which an educated person sees as he reads, just as you and I see Latin, German and Greek roots.