My Canadian SIN card is a tidy, official-looking piece of plastic, white, with a thin, tasteful border of red around the edge, and a faded seal of the appropriate governmental agency in the background. My name and number are printed on it in indeliable black, letters slender and tidy and tasteful.
My UK NI card came today. It's jauntily colored, a crimson and blue piece of plastic. So bright! So raucous! With big, bold letters so I can read it halfway across the room! And letters and numbers in relief so paper can be embossed on it. It's a whole different concept of what a card-with-a-number-on-it is for.