The first 3,000 people who register their 3DS in Europe with Club Nintendo will be getting a t-shirt with the question-mark AR Card placed on the front of it. This means that 3DS owners will be able to use the 3DS to make augmented reality art on their own T-Shirts, or on other people if they have them wear it instead. Either way though, it would require the person wearing the shirt to stand still the entire time.
Registering the 3DS itself will give Club Nintendo members 750 points right off the bat. So perhaps one of the first things you should do after you get home is hop onto your computer and type in that code to make sure you end up with a T-Shirt in Europe.