As a brand gets recognized globally you can see several copies of that brand in the market. Ray-Ban is also one of them. So how can you tell if a Ray-Ban is real or fake? 

Here are some prime factors which you should look while figuring out if your Ray-Ban is real or not:

Quality and Finish
Quality of lens
Hinges
Nose pads 
Packaging

As the original Ray-Ban is made by hand in Italy so it is an obvious thing that the quality and most important their packaging are on point. Hold on your Ray-Ban and do a little Quality check. If the Quality of the lens is satisfying,  the finish which you see around joints is of good quality. The real Ray-Ban's are hand made and polished from a real block of very high-quality acetate. 

Check the lens the real Ray-Ban has their "RB" logo sculpted in one of their lenses. 
http://www.theeyecentre.com/how-can-i-tell-if-a-ray-ban-is-real-or-fake.html#:~:text=All%20original%20Ray%2DBans%20have,and%20etched%2C%20not%20painted%20on.