We have seen a few of these envelope laptops sleeves before, particularly for the MacBook Air, now there is a new version available which is designed to disguise your laptop with a worn envelope, and protect it from thieves.
Turn your laptop into something that any opportunist thief would not look twice at. Looking like a tatty old envelope the Undercover Laptop Sleeve is a state of the art laptop sleeve, both waterproof and tear proof whilst also providing padding to stop your laptop from getting damaged.
The Undercover Laptop Sleeve is available in two sizes and it will take laptops from 8-13 inches or from 13-17 inhces, and it is designed to be tearproof and watperproof and features some extra padding to protect your laptop.
If you want one they are available for $29.79 from Lazybone.