How do I identify Honda Z50R from Chinese copy?

Just bought a cheap monkey bike fitted with what appears to be a Honda engine.It has a Honda logo on left side outer cover. Seller claimed it was a Honda but I can't be certain. It has no plate on frame although there are a couple of rivets which look like they held a vin. tag, on the headstock. Bike has several coats of paint but there is red showing through and mudguards were originally red.Are there any obvious telltales?Should frame be stamped with a number, and if so, where were they stamped?