Below are a few examples of what are called "Test Notes". As their name implies, these curiosities were made by printing companies in testing the printing methods, and for use in ATM and other cash handling machines. Generally, the more artistic the images are, they can be assumed that they were made to test the printing abilities, methods, etc. Those which are less artful, are for use in testing the machines abilities.
Here are some from the printer Thomas De La Rue. Obviously these were made primarily to test machines or to be given out as advertising pieces to customers.
Here are some more from Thomas De La Rue with a more artistic bent:
These are printed by Arcatech Systems:
This last note, a gift from a fellow IBNS member, is an experimental note printed specially for the 1995 London IBNS Congress: