Ulysse Nardin Maxi Marine Chronograph

Quick question apart from the serial number at the 6,how eles can you identify a omega,reason i ask my friend had an old gmt pepsi on last week he just bought it from ebay,has box but no papers (already told him he is an idiot) can't make out the serial number,i told him this does not look good,but it is a genuine omega,so if he opens it up can he identify the watch ?........

I don't want that this thread end in argument. But there are some controversy that I see in many watch fans in different forums. My question. Is a chronograph a dress watch that you would put with a suit at your office?Many would say, no. A dress watch is a simple white dial with three hands, without date window. But when people talk about omega, omega, tag they consider any of their expensive chronograph purchases as a dress watch. Any patek can be a dress watch whatever model it is because it ........