The official FMA watch has an engraved cover 
instead of an embossed one, and the watch face 
features a very cute picture of the Elric 
brothers.

Unfortunately since so few of the official ones 
were made, a lot of people started selling fakes 
to cash in on the series.  ;_;  It's okay if you 
just want to cosplay, but be careful what you buy 
if you want to collect.

As a side note, there don't seem to be any 
auctions running on Yahoo Japan right now for the 
real watch.