where to register my product?

I bought my first board about 3 years ago and don't remember if 'registration' was an option back then.
I have just acquired a new UNO R3 which has a product code I can register.
However, search as I have I can find nowhere to register my board. I also cannot find a Forum post mentioning it.
Can anyone direct me to where I can register my board please?

Here's an official response to the same question when it was asked a while ago:
http://forum.arduino.cc/index.php?topic=491337.msg3356189#msg3356189