$10 millennium note security features

One of the security features on the $10 millennium notes is a special "see-through" window. If you fold the bank note over and look through the clear window at the map of New Zealand next to the canoe, the letters `Y2K' become visible. This is illustrated in the picture above.
Another innovative security feature is the two silver ferns within the clear window, which reflect rainbow colours when you tilt the note to the light.
These are in addition to the security features found on other polymer bank notes, such as a watermark (shadow image), microprinting, fluorescent patches, raised printing and serial numbers. For more information on the security features of polymer bank notes, take a look at the pamphlet The New Polymer Bank Notes (115Kb).
If you're having difficulties seeing the Y2K feature, these other security features can be used to confirm the validity of the bank note.