Yes, the cartier sunglasses have the serial numbers on the trade mark which is hung on the frame side. If you want to judge whether it is real, you could call the cartier sunglasses center to check with the client about the serial number. It is so easy that you just need to make a call.
Well, as you can see, cartier is one of the most amazing fashion brands in the world and it holds a great reputation for everything they have provided, including their nice sunglasses. On general, you may find some certificate or serial numbers that can prove its authenticity. In the mean time, you might as well contact their customer department for help. Just call their hotlines and see if what they can do.
Cartier is a well-known luxury brand. Yet it is difficult to tell whether it is not authentic. It will not cost the money if it is just a fake one. There are some marks on Cartier products to distinguish it from the fraud. The first step, you could check the screws in frames. There are only metal ones. Secondly, there are serial number started with 2. It should be graved finely in very tiny numbers.
Thirdly, check if there is bar code on the nose piece of the frames. Be careful with all the checking items above. Hope you can find the authentic sunglasses you liked.