Well, as a matter of fact, you should know Chanel is one of the most luxurious products. Their company is always trying to tackle fake products, therefore, serial numbers becomes one of their ways to protect their interest. Generally speaking, it would get it once you carefully check the certificate and follow the instruction. Or you may just contact their customer department for help.
In order to be copied by other maufacturers, many great brands of sunglasses have serial numbers. However, some fakes can come with serial numbers etched on the lens. So real Chanel sunglasses do not have a space after the first two characters of the serial numbers. Chanel sunglasses' model number and color code should be printed on the inside left arm. And the model number is always four digits which may be followed by a dash and a letter and the color code is always three or four digits followed by a backslash and two more digits. For example: 5076-H (model number) 501/87 (color code).
Yes, every pair of real chanel sunglasses have the serial numbers. It can be used to spot if they are real or fake. As we all known, Chanel is one of the most luxurious products in the world, thus serial numbers is one of their ways to protect their interest. You can identify it by surfing their official website.