MacBook Air\Pro Engraving?

Sure if can be done, but Apple won't do it. They only do it for iPads or the iPod Touch.

Engraving and Gift Wrap - Apple

I'm pretty sure there are 3rd party companies that will do laser engraving.

https://store.ipadlaserengraving.com/create_products/Engraved-MacBook-Pro?n=7965 63

I think you could, though what do you want to engrave on surface of MacBook Air/Pro?