if it says 'peice of eight' on it,its a copy.
The original peices of eight were the predecessors of our own silver
dollars.the 'M' on it indicates it was minted in Mexico City.They were also
minted throughout the central and south American possessions of the Spanish
Empire between (help me out here,everyone) 1632 and 1800 (approximately).
some of our better-informed friends here can give much more,detailed
info,but basically,it sounds like a copy made for tourists.