If you plan on selling it, which I hope you don't because you're never going to get your fair hourly rate back(for building it), then you need to make the buyer aware that it is a replica, or clone. You may be able to get that to slide once or twice, but if you make a habit of it, UA is going to be contacting you for some money.
If it's just to wow clients coming in the door, do what you like. A water slide decal could work, but I would go for a vinyl decal, printed and cut for you professionally, it will last longer and look more like a silk-screen.